MIPS: add kmap_noncoherent to wire a cached non-coherent TLB entry

This is identical to kmap_coherent apart from the cache coherency
attribute used for the TLB entry, so kmap_coherent is abstracted to
kmap_prot which is then called for both kmap_coherent &
kmap_noncoherent. This will be used by a subsequent patch.

Suggested-by: Leonid Yegoshin <leonid.yegoshin@imgtec.com>
Signed-off-by: Paul Burton <paul.burton@imgtec.com>

diff --cc arch/mips/include/asm/cacheflush.h
Simple merge

diff --cc arch/mips/include/asm/pgtable.h
Simple merge

diff --cc arch/mips/mm/init.c
Simple merge