MIPS ioremap cleanups v2

From: Christoph Hellwig
Date: Thu Apr 16 2020 - 11:00:30 EST


Hi Thomas,

below is a bunch of cleanups for the MIPS ioremap code. Compile tested
only.

Changes since v1:
- don't remove cpu_has_64bit_gp_regs
- add a new prep patch to stop txx9aclc-ac97 from poking into ioremap
internals