We should apply watermark_sclae_factor after
boot complete. Otherwise, extra_free_kbytes.sh
might overwrite it and this also aligns with
previous projects' timing.
Bug: 278075546
Test: boot and check watermark_scale_factor
Change-Id: I7989fd1e8cd968193577300b0f83a829bdeb037d
Signed-off-by: Martin Liu <liumartin@google.com>