tty: Added a CONFIG_TTY option to allow removal of TTY

The option allows you to remove TTY and compile without errors. This
saves space on systems that won't support TTY interfaces anyway.
bloat-o-meter output is below.

The bulk of this patch consists of Kconfig changes adding "depends on
TTY" to various serial devices and similar drivers that require the TTY
layer.  Ideally, these dependencies would occur on a common intermediate
symbol such as SERIO, but most drivers "select SERIO" rather than
"depends on SERIO", and "select" does not respect dependencies.

bloat-o-meter output comparing our previous minimal to new minimal by
removing TTY.  The list is filtered to not show removed entries with awk
'$3 != "-"' as the list was very long.

add/remove: 0/226 grow/shrink: 2/14 up/down: 6/-35356 (-35350)
function                                     old     new   delta
chr_dev_init                                 166     170      +4
allow_signal                                  80      82      +2
static.__warned                              143     142      -1
disallow_signal                               63      62      -1
__set_special_pids                            95      94      -1
unregister_console                           126     121      -5
start_kernel                                 546     541      -5
register_console                             593     588      -5
copy_from_user                                45      40      -5
sys_setsid                                   128     120      -8
sys_vhangup                                   32      19     -13
do_exit                                     1543    1526     -17
bitmap_zero                                   60      40     -20
arch_local_irq_save                          137     117     -20
release_task                                 674     652     -22
static.spin_unlock_irqrestore                308     260     -48

Signed-off-by: Joe Millenbach <jmillenbach@gmail.com>
Reviewed-by: Jamey Sharp <jamey@minilop.net>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/class/Kconfig

@@ -6,7 +6,7 @@ comment "USB Device Class drivers"
 
 config USB_ACM
 	tristate "USB Modem (CDC ACM) support"
-	depends on USB
+	depends on USB && TTY
 	---help---
 	  This driver supports USB modems and ISDN adapters which support the
 	  Communication Device Class Abstract Control Model interface.

drivers/usb/gadget/Kconfig

@@ -750,6 +750,7 @@ config USB_GADGET_TARGET
 
 config USB_G_SERIAL
 	tristate "Serial Gadget (with CDC ACM and CDC OBEX support)"
+	depends on TTY
 	select USB_LIBCOMPOSITE
 	help
 	  The Serial Gadget talks to the Linux-USB generic serial driver.
@@ -799,6 +800,8 @@ config USB_G_PRINTER
 	  For more information, see Documentation/usb/gadget_printer.txt
 	  which includes sample code for accessing the device file.
 
+if TTY
+
 config USB_CDC_COMPOSITE
 	tristate "CDC Composite Device (Ethernet and ACM)"
 	depends on NET
@@ -879,6 +882,8 @@ config USB_G_MULTI_CDC
 
 	  If unsure, say "y".
 
+endif # TTY
+
 config USB_G_HID
 	tristate "HID Gadget"
 	select USB_LIBCOMPOSITE
@@ -895,6 +900,7 @@ config USB_G_HID
 # Standalone / single function gadgets
 config USB_G_DBGP
 	tristate "EHCI Debug Device Gadget"
+	depends on TTY
 	select USB_LIBCOMPOSITE
 	help
 	  This gadget emulates an EHCI Debug device. This is useful when you want

drivers/usb/serial/Kconfig

@@ -4,7 +4,7 @@
 
 menuconfig USB_SERIAL
 	tristate "USB Serial Converter support"
-	depends on USB
+	depends on USB && TTY
 	---help---
 	  Say Y here if you have a USB device that provides normal serial
 	  ports, or acts like a serial device, and you want to connect it to