drm/amd/display: Request 0MHz dispclk for zero display case

[Why]
If we aren't entering RCG/IPS2 or CLKSTOP is not supported by PMFW then
we should be requesting a dispclk value of 0MHz to PMFW.

Currenly we run at max clock since there's an assumption in APU clock
table formulation where we can run at any DISPCLK at any state so the
real clock value ends up as 1200Mhz - the maximum.

[How]
Set to 0 instead of the minimum value in the state array.

Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Reviewed-by: Duncan Ma <duncan.ma@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Rodrigo Siqueira <rodrigo.siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>