msm_fb: HDMI: Driver changes to support MHL boot param

Add necessary driver changes to support enabling MHL using
a boot parameter. The MHL driver will now only be used if it
is enabled using the boot parameter. If enabled, the default
video resolution and available EDID modes will be set
accordingly.

Change-Id: I9c07a4bdd07ce1d9120296efb143e987390fa0a2
Signed-off-by: Aravind Venkateswaran <aravindh@codeaurora.org>