drm/amd/display: support 48 MHZ refclk off

drm/amd/display: support 48 MHZ refclk off

[Why]
On PCO and up, whenever SMU receive message to indicate active
display count = 0. SMU will turn off 48MHZ TMDP reference clock
by writing to 1 TMDP_48M_Refclk_Driver_PWDN. Once this clock is
off, no PHY register will respond to register access. This means
our current sequence of notifying display count along with requesting
clock will cause driver to hang when accessing PHY registers after
displays count goes to 0.

[How]
Separate the PPSMC_MSG_SetDisplayCount message from the SMU messages
that request clocks, have display own sequencing of this message so
that we can send it at the appropriate time.
Do not redundantly power off HW when entering S3, S4, since display
should already be called to disable all streams. And ASIC soon be
powered down.

Signed-off-by: Eric Yang <Eric.Yang2@amd.com>
Reviewed-by: Tony Cheng <Tony.Cheng@amd.com>
Acked-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>