MLK-13862-1 epdc/pxp: imx7d: enhance the LUT cleanup flow to avoid stalling display

- change from wfe_b to wfe_a, and modifiy register settings to support new flow
- the underlying design policy change as follows.
  in previous flow, when all LUTs are used, the LUT cleanup operation
  need to wait for all the LUT to finish, it will not happen util last LUT
  is done. while in new flow, the cleanup operation does not need to wait
  for all LUTs to finish, instead it can start when there's LUT's done.
  The saved time is multiple LUT operation time.

Signed-off-by: Robby Cai <robby.cai@nxp.com>
(Vipul: Fixed merge conflicts)
Signed-off-by: Vipul Kumar <vipul_kumar@mentor.com>
Signed-off-by: Srikanth Krishnakar <Srikanth_Krishnakar@mentor.com>