msm: sde: enable rotator interrupt only if irq is defined

Rotator regdma interrupt is enabled during fetch engine
configuration even if irq is not defined. Even though
the interrupt will be cleared by the polling loop after
exit, it will generate constant interrupt request for
the master interrupt controller from the time interrupt
fires to the time the interrupt is cleared at the end of
the polling loop. Modify fetch configuration to enable
rotator interrupt only if irq is defined.

Change-Id: I7d1710463ef3017519a22dc95ddb40b896f553a5
Signed-off-by: Alan Kwong <akwong@codeaurora.org>