[ALSA] PCM midlevel & PCM OSS - make procfs & OSS plugin code optional

Modules: ALSA Core,PCM Midlevel,ALSA<-OSS emulation,USB generic driver

1) The verbose procfs code for the PCM midlevel and usb audio
   can be removed now (more patches will follow).
   CONFIG_SND_VERBOSE_PROCFS
2) The PCM OSS plugin system can be also compiled optionaly.
   CONFIG_SND_PCM_OSS_PLUGINS

Signed-off-by: Jaroslav Kysela <perex@suse.cz>