disp: msm: sde: avoid irq enable/disable during modeset

Avoid irq enable/disable during modeset and trigger
frame as posted start frame. This saves mode_set time
and also avoids unbalanced vblank_irq in this usecase.

Change-Id: I06958da5e52bc2aca0ddc60d2783615f80a839a4
Signed-off-by: Dhaval Patel <quic_pdhaval@quicinc.com>
Signed-off-by: Jayaprakash Madisetty <quic_jmadiset@quicinc.com>