usb: Provide usb_speed_string() function

In a few places in the kernel, the code prints
a human-readable USB device speed (eg. "high speed").
This involves a switch statement sometimes wrapped
around in ({ ... }) block leading to code repetition.

To mitigate this issue, this commit introduces
usb_speed_string() function, which returns
a human-readable name of provided speed.

It also changes a few places switch was used to use
this new function.  This changes a bit the way the
speed is printed in few instances at the same time
standardising it.

Signed-off-by: Michal Nazarewicz <mina86@mina86.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/usb/Kconfig

@@ -12,6 +12,11 @@ menuconfig USB_SUPPORT
 
 if USB_SUPPORT
 
+config USB_COMMON
+	tristate
+	default y
+	depends on USB || USB_GADGET
+
 # Host-side USB depends on having a host controller
 # NOTE:  dummy_hcd is always an option, but it's ignored here ...
 # NOTE:  SL-811 option should be board-specific ...