drm/msm/dpu: relax parameter validation in encoders

drm/msm/dpu: relax parameter validation in encoders

DPU, being over protective, validates every parameter of a
module. This change traces the call stack for some of encoder
functions affected by previous set of clean up patches and
cleans up unwanted validations.

changes in v5:
	- Introduced in the series
changes in v6:
	- none

Signed-off-by: Jeykumar Sankaran <jsanka@codeaurora.org>
Reviewed-by: Sean Paul <seanpaul@chromium.org>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Signed-off-by: Rob Clark <robdclark@gmail.com>