msm8974: mhl: enable tmds stream on powered dongle

Enable TMDS stream and MHL-HPD only when MHL TX is connected
to a powered dongle. This information is read from the sink/dongle's
device capability bytes. The MHL Tx prevents outgoing TMDS stream
on an unpowered dongle which saves power drainage.
On connection to an unpowered dongle during the initial discovery
rgnd discovery reports MHL, subsequently, uUSB is reported. Set
HPD/TMDS low at this point without handing over the control to
USB driver. This enables detection of interrupts in MHL driver
but prevents TMDS signals from being sent to the sink.

Change-Id: I5f13880caff7fe852952b55763d53224e3146ebd
CRs-Fixed: 494771
Signed-off-by: Manoj Rao <manojraj@codeaurora.org>