msm: mdss: hdmi: add support for triggering hot plug

Add sysfs node to trigger cable disconnect/connect hot plug
interrupts. Power off 5v regulator which provides 5v to sink
which in turn pulls hpd line low resulting in disconnect hot
plug interrupt. Similarly, power on 5v regulator to get connect
hot plug interrupt. This is needed to simulate cable connect
and disconnect for some special requirements like resolution
switch from the user applications.

Change-Id: I882358ddb40acf07a5e7be692aac590880e012c2
Signed-off-by: Ajay Singh Parmar <aparmar@codeaurora.org>