disp: msm: sde: move qsync validation to encoder atomic check

In connector atomic check, seamless vrr cannot be
determined since mode doesn't get populated by that time.
This change moves qsync validation from connector to encoder
atomic check to verify & handle modeset concurrencies.

Change-Id: Ia41bde4c05f98d8ba4cb39c18f2da1683cf9e5a3
Signed-off-by: Yashwanth <yvulapu@codeaurora.org>