MIPS: Loongson: Fix the write-combine CCA value setting

All Loongson-2/3 processors support _CACHE_UNCACHED_ACCELERATED, not
only Loongson-3A.

Signed-off-by: Huacai Chen <chenhc@lemote.com>
Cc: John Crispin <john@phrozen.org>
Cc: Steven J. Hill <Steven.Hill@imgtec.com>
Cc: linux-mips@linux-mips.org
Cc: Fuxin Zhang <zhangfx@lemote.com>
Cc: Zhangjin Wu <wuzhangjin@gmail.com>
Patchwork: https://patchwork.linux-mips.org/patch/8319/


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