msm: mdss: use irq type in PM QOS vote for DSI

In the current implementation, all CPUs are switched
on when PM QOS vote is requested from DSI.

Switching to irq based vote for QOS request, as this will
let other CPUs to go into idle PC apart from the CPU to
which the IRQ's affinity is set to.

Change-Id: I453fe21b19dc7771075006b986a9040c2f8285fe
Signed-off-by: Kalyan Thota <kalyant@codeaurora.org>