mm: Change munmap splitting order and move_vma()

mm: Change munmap splitting order and move_vma()

Splitting can be more efficient when done in the reverse order to
minimize VMA walking.  Change do_mas_align_munmap() to reduce walking of
the tree during split operations.

move_vma() must also be altered to remove the dependency of keeping the
original VMA as the active part of the split.  Look up the new VMA or
two if necessary.

Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>