MIPS: Alchemy: remove au_read/write/sync

replace au_read/write/sync with __raw_read/write and wmb.

Signed-off-by: Manuel Lauss <manuel.lauss@gmail.com>
Cc: Linux-MIPS <linux-mips@linux-mips.org>
Patchwork: https://patchwork.linux-mips.org/patch/7465/


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