drm: msm: sde: fix decimation validation in plane atomic_check

Fix the invalid decimation check which skips the validations
below when decimation is enabled. This fails to validate
few parameters and also miss updating few state variables
leading to various issues. Part of the change add an event
log to track when the driver qseed/PE settings are used.

Change-Id: Id0c23f5097f0d8d161ca1366a1522d243810e152
Signed-off-by: Raviteja Tamatam <travitej@codeaurora.org>