drm/msm/dsi: Move PHY operations out of host

Since DSI PHY has been a separate platform device, it should not
depend on the resources in host to be functional. This change is
to trigger PHY operations in manager, instead of host, so that
host and PHY can be completely separated.

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