msm: sde: notify driver client of resource allocation failure

Events can be registered by the driver clients using the custom event
registration ioctl.If display is not powered on when custom ioctl is
called, registration fails.Currently driver notifies user-space client
invalid error,instead it should notify that resources are not allocated
for display so that user-space client can retry.

Change-Id: Ia6e35c8c32bf00dbe2ef51b13092edf7bf5f41f7
Signed-off-by: Xu Yang <yangxu@codeaurora.org>
Signed-off-by: Gopikrishnaiah Anandan <agopik@codeaurora.org>