drm/amd/display: limit display clock to 100MHz to avoid FIFO error

[Why]
when changing display clock, SMU need to use power up DFS and use
DENTIST to ramp DFS DID to switch target frequency before switching back
to bypass.

[How]
fixed the minimum display clock to 100MHz, it's W/A the same with PCO.

Signed-off-by: Yu-ting Shen <Yu-ting.Shen@amd.com>
Reviewed-by: Tony Cheng <Tony.Cheng@amd.com>
Acked-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Acked-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>