[PATCH] build sound/sound_firmware.c only for OSS

All sound/sound_firmware.c contains is mod_firmware_load() that is a legacy
API only used by some OSS drivers.

This patch builds it into an own sound_firmware module that is only built
depending on CONFIG_SOUND_PRIME making the kernel slightly smaller for ALSA
users.

[alan@lxorguk.ukuu.org.uk: comment fix]
Signed-off-by: Adrian Bunk <bunk@stusta.de>
Acked-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Alan Cox <alan@redhat.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>