linuxdriver: add Watermark flush mechanism [2/2]

PD#SWPL-36395

Problem:
1) if Verimatrix Watermark enable, OSD flicker when the TV station changes
2) if screen resolution changes, NexGuard Watermark display is abnormal

Solution:
add Watermark flush mechanism

Verify:
Android Q + AH212(SC2)

Change-Id: I096ecf01eca522cb3b6c2f943cd57ab813eb92ed
Signed-off-by: Liqiang Jin <liqiang.jin@amlogic.com>