ALSA support for the SEGA Dreamcast Yamaha AICA sound device (pcm)

This patch adds ALSA sound support for pcm playback on two channels on
the SEGA Dreamcast built-in sound device (the Yamaha AICA)

Add driver for the AICA sound device built into the SEGA Dreamcast

Hook it all up with the build system.

Signed-off-by: Adrian McMenamin <adrian@mcmen.demon.co.uk>