drm/amd/display: Add interface to track PHY state

[Why]
Sometimes pixel clock needs to remain active after transmitter disable.

[How]
Use update_phy_state to track PHY state after stream
enable/disable and program pixel clock as needed.

Reviewed-by: Alvin Lee <alvin.lee2@amd.com>
Acked-by: Brian Chang <Brian.Chang@amd.com>
Signed-off-by: Taimur Hassan <Syed.Hassan@amd.com>
Signed-off-by: Alvin Lee <alvin.lee2@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>