sound: Disable the build of OSS drivers

OSS drivers are left as badly unmaintained, and now we're facing a
problem to clean up the hackish set_fs() usage in their codes.  Since
most of drivers have been covered by ALSA, and the others are dead old
and inactive, let's leave them RIP.

This patch is the first step: disable the build of OSS drivers.
We'll eventually drop the whole codes and clean up later.

Note that sound/oss/dmasound is still kept, since it's a completely
different implementation of OSS, and it doesn't suffer from set_fs()
hack.  Moreover, the build of ALSA is disabled on M68K by some reason,
thus disabling it shall result in a regression.  This one will be
disabled / removed once when we add the support in ALSA side.

Tested-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>