drm/amd/display: workaround for HDMI hotplug in DPMSOFF state

[Why]
When hotplug a HDMI monitor during entering S0i3 or DPMSOFF state due to
entering infinite loop when calling vbios to program pixel clocks. In
this scenario, pll is enabled but phy is not, and there is not a
programing guide for this case.

[How]
Before we having the proper programing guide, before disable pll, doing
a phy enable and disable to avoid the issue.

Signed-off-by: Yongqiang Sun <yongqiang.sun@amd.com>
Reviewed-by: Tony Cheng <Tony.Cheng@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>