drm/amd/display: implement dc_mode_memclk

why:
Need interface to lower clocks when in dc (power save)
mode. Must be able to work with p_state unsupported cases
Can cause flicker when OS notifies us of dc state change

how:
added dal3 interface for KMD
added pathway to query smu for this softmax
added blank before clock change to override underflow
added logic to change clk based on pstatesupport and softmax
added logic in prepare/optimize_bw to conform while changing
clocks

Reviewed-by: Aric Cyr <Aric.Cyr@amd.com>
Acked-by: Pavle Kotarac <Pavle.Kotarac@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Martin Leung <Martin.Leung@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>