drm/msm/dsi: Reset both PHYs before clock operation for dual DSI

In case of dual DSI, some registers in PHY1 have been programmed
during PLL0 clock's set_rate. The PHY1 reset called by host1 later
will silently reset those PHY1 registers. This change is to reset
and enable both PHYs before any PLL clock operation.

[Originally worked on by Hai Li <hali@codeaurora.org>. Fixed up
by Archit Taneja <architt@codeaurora.org>]

Signed-off-by: Archit Taneja <architt@codeaurora.org>
Signed-off-by: Rob Clark <robdclark@gmail.com>