[ALSA] Decentralize PM control

Modules: ALSA Core,Control Midlevel,/oss/Makefile

Remove the centralized PM control in the sound core.
Each driver is responsible to get callbacks from bus/driver now.

SND_GENERIC_DRIVER is removed together with this action.

Signed-off-by: Takashi Iwai <tiwai@suse.de>