drm/msm/dp: assert phy reset before phy mode switch on trinket

The qmp-phy is shared by ssusb and Displayport for phy operations.
The phy and pll reset lines should be asserted when switching the
qmp-phy to Displayport mode. Failing to do so is causing the
Displayport PLL to not correctly lock to the requested link clock
frequency. These changes will assert the phy reset, switch the phy
mode to Displayport mode and then deassert the phy reset to help
correctly lock the Displayport PLL.

Change-Id: I66203000ef3d8b0b2f5e0c6fe3f7e784c9fc6bf5
Signed-off-by: Sankeerth Billakanti <sbillaka@codeaurora.org>