drm/msm/sde: add interrupt enabling state to fix deadlock

Add one more state of interrupt enabling as transition state
when enable the interrupt. Change fixes the deadlock issue
when client tries to enable the interrupt and meanwhile there
is interrupt callback function happenes.

CRs-Fixed: 2316684
Change-Id: I2954db910df1e63d5882e7980f01b9219647e731
Signed-off-by: Xu Yang <yangxu@codeaurora.org>