Revert "BACKPORT: mm: move zone watermark accesses behind an accessor"

This reverts commit acfb1c60.

Reason for revert: revert customized code
Bug: 140544941
Test: boot
Signed-off-by: Minchan Kim <minchan@google.com>
Signed-off-by: Martin Liu <liumartin@google.com>
Signed-off-by: Mark Salyzyn <salyzyn@google.com>
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Change-Id: I4988ddf1fc24579d4fc478de1de6e45b870f7bcd