drm/msm: update irq registration during seamless mode switch

IRQ table can be updated during seamless mode switch. Encoder
should release existing irq mapping before mode set and update
irq mapping according to new mode set. Update encoder mode set
callback to perform irq unregistration before new resource
reservation, perform new irq registration after. Move wait
for tx complete to mode set so that resource is only
released after last transmission is complete.

Change-Id: Ic1a641d1cce3e2460b95fa8573f0f272cdcf54cc
Signed-off-by: Alan Kwong <akwong@codeaurora.org>
Signed-off-by: Dhaval Patel <pdhaval@codeaurora.org>