linux-yocto: enable audio for selected qemu targets

linux-yocto: enable audio for selected qemu targets

Fixes [BUGID #488 #734]

Enable audio for qemux86/qemux86-64 via the following kernel
configuration options.

  CONFIG_SOUND_OSS_CORE=y
  CONFIG_SOUND_OSS_CORE_PRECLAIM=y
  CONFIG_SND_RAWMIDI=m
  CONFIG_SND_SEQUENCER=y
  CONFIG_SND_OSSEMUL=y
  CONFIG_SND_MIXER_OSS=y
  CONFIG_SND_PCM_OSS=y
  CONFIG_SND_PCM_OSS_PLUGINS=y
  CONFIG_SND_SEQUENCER_OSS=y
  CONFIG_SND_RAWMIDI_SEQ=m
  CONFIG_SND_AC97_CODEC=m
  CONFIG_SND_ENS1370=m
  CONFIG_SND_INTEL8X0=m
  CONFIG_AC97_BUS=m

The mechanism to trigger these options is in the form of an
optional kernel feature that is only appended for qemux86
and qemux86-64, but is contained within the kernel tree.

This allows several things:

  - the options to be available/shared for all boards
  - the options to be in tree
  - to not add the options to every board, which unecessarily
    bloats the default configuration.

Signed-off-by: Bruce Ashfield <bruce.ashfield@windriver.com>