disp: msm: fix probe deferral logic

msm_drv should be probe deferred until rsc driver
probe is done. OF_POPULATED flag only checks if platform
driver is registered and hence additional condition to
check if driver is attached to this device, is needed.

Change-Id: I070965cc8d3ba3984032ad3704ec86066680eef0
Signed-off-by: Abhijit Kulkarni <kabhijit@codeaurora.org>