Optimize RegionSpace::ClearFromSpace()

We perform madvise() and mprotect() syscalls in
RegionSpace::ClearFromSpace() for every region that we reclaim. This was
being done while holding region_lock_. This has the potential to stall
the TLAB allocation requests.
In this CL, we pull out system calls out of the critical section of
region_lock_.

Bug: 132463704
Test: art/test/testrunner/testrunner.py --host --debug

(cherry picked from commit baa99adfc7154a9d8b12736752e44e199a5fbbf0)

Merged-In: Ie9e96c95a7ee78a9b18c1bfc26ed04acbe99c32b
Change-Id: Ie9e96c95a7ee78a9b18c1bfc26ed04acbe99c32b