msm: mdss: fix the dead lock in the MDP3 irq handling

A deadlock can occur when an interrupt happens while a user thread
holds a spin lock and tries to call irq_disable, which waits until
the interrupt is serviced.

Change-Id: I350547800c79a4cdb3feb281d9a872248c137d57
Signed-off-by: Xiaoming Zhou <zhoux@codeaurora.org>