mm/mmap: Alter brk to be more maple tree efficient.

mm/mmap: Alter brk to be more maple tree efficient.

Alter the brk, do_brk_flags() calls and add do_brk_munmap() to be more
efficient when using the maple tree.

kvm Benchmark on 8 core laptop:
./mmtests/work/sources/wis-0-installed/brk1_threads

rb_tree v5.9-rc1:
min:3633758 max:3633758 total:3633758
min:3604892 max:3604892 total:3604892
min:3589182 max:3589182 total:3589182
min:3581230 max:3581230 total:3581230

maple tree with this patch:
min:3673408 max:3673408 total:3673408
min:3659268 max:3659268 total:3659268
min:3624968 max:3624968 total:3624968
min:3613576 max:3613576 total:3613576

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