Add sound driver using audsrv.irx.
Some small cleanups regarding RPC.
Detect automatically whether IRX module is loaded from "rom0:", "rom1:" or
Linux hotplug /lib/firmware.
Add possibilty to directly load audsrv.irx at startup when it is added to the
kernel, e.g. by the kernel configuration in .config:
CONFIG_FIRMWARE_IN_KERNEL=y
CONFIG_EXTRA_FIRMWARE="audsrv.irx"
CONFIG_EXTRA_FIRMWARE_DIR="/usr/local/ps2dev/ps2sdk/iop/irx/"