IPRA: Run RegUsageInfoPropagate much later

This was running immediately after isel, before
isel pseudos were even expanded which is really
unreasonable. Move this to before pre-reglloc
passes in case some other pre-regalloc pass wants to
use the updated regmask info.

Fixes one of the reasons IPRA doesn't do anything on
AMDGPU currently. Tests will be included with future
patch after a few more are fixed.

llvm-svn: 310875