msm: mdss: hdmi: add support for custom edid

Add sysfs node to provide a custome EDID to HDMI driver to
address some special requirements from user applications like
switching to a custom EDID in cases where sink doesn't support
EDID or DDC line to read EDID.

Change-Id: I75726e28722aa128cfc315b3b1b0e97e9a9cde56
Signed-off-by: Ajay Singh Parmar <aparmar@codeaurora.org>