msm_fb: MHL: Fix premature register access

Until the information about the MHL feature through
boot param percolates to the driver via probe we should
refrain from accessing the registers or requesting irq.
The init and probe functions are cleaned up with all
the real initialization such as power, gpio and chip
specific settings moving to probe functionality only
if mhl is enabled from boot param.

Change-Id: I68c0a2848493a7478f3046e439c42f8fb131f000
Signed-off-by: Manoj Rao <manojraj@codeaurora.org>