MIPS: inline mips_init_[id]cache functions

MIPS: inline mips_init_[id]cache functions

The mips_init_[id]cache functions are small & only called once from a
single callsite. Inlining them allows mips_cache_reset to avoid having
to bother moving arguments around & leaves it a leaf function which is
thus able to simply keep the return address live in the ra register
throughout, simplifying the code.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Cc: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>