msm: vidc: Enable/disable irq in power on/off functions

Video driver should enable IRQs as soon as we have IRQ handling
setup on the host side and as soon as venus is powered up.
Reverse is true for power down.

Change-Id: Id5ea03f4f1246425bcadf15b05ef5e587f238dad
Signed-off-by: Vinay Kalia <vkalia@codeaurora.org>