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: I829d54d6b77b1ff39827b08a28f7edbb98ed8e24
Signed-off-by: Veera Sundaram Sankaran <veeras@codeaurora.org>