[POWERPC] Update MPC8610 HPCD to support audio drivers

Update the MPC8610 HPCD files to support the audio driver.  Update
booting-without-of.txt with information on the SSI device.

Signed-off-by: Timur Tabi <timur@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>