ALSA: jack: Allow building the jack layer without input device

Since the recent integration of kctl jack and input jack layers, we
can basically build the jack layer even without input devices.  That
is, the jack layer itself can be built with conditional to enable the
input device support or not, while the users may enable always
CONFIG_SND_JACK unconditionally.

For achieving it, this patch changes the following:
- A new Kconfig, CONFIG_SND_JACK_INPUT_DEV, was introduced to indicate
  whether the jack layer supports the input device,
- A few items in snd_jack struct and relevant codes are conditionally
  built upon CONFIG_SND_JACK_INPUT_DEV,
- The users of CONFIG_SND_JACK drop the messy dependency on
  CONFIG_INPUT.

This change also automagically fixes a potential bug in HD-audio
driver Arnd reported, where the NULL or uninitialized jack instance is
dereferenced.

Reported-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/pci/Kconfig

@@ -866,7 +866,7 @@ config SND_VIRTUOSO
 	select SND_OXYGEN_LIB
 	select SND_PCM
 	select SND_MPU401_UART
-	select SND_JACK if INPUT=y || INPUT=SND
+	select SND_JACK
 	help
 	  Say Y here to include support for sound cards based on the
 	  Asus AV66/AV100/AV200 chips, i.e., Xonar D1, DX, D2, D2X, DS, DSX,

sound/pci/hda/Kconfig

@@ -4,7 +4,7 @@ config SND_HDA
 	tristate
 	select SND_PCM
 	select SND_VMASTER
-	select SND_JACK if INPUT=y || INPUT=SND
+	select SND_JACK
 	select SND_HDA_CORE
 
 config SND_HDA_INTEL