MIPS: Alchemy: au1000.h: remove unused register definitions

Remove the unused SSI I2S and AC97C register definitions.

Signed-off-by: Manuel Lauss <manuel.lauss@gmail.com>
Cc: Linux-MIPS <linux-mips@linux-mips.org>
Patchwork: https://patchwork.linux-mips.org/patch/7462/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>