drm/amd/display: adjust MALL size available for DCN32 and DCN321

drm/amd/display: adjust MALL size available for DCN32 and DCN321

[Why]
MALL size available can vary for different SKUs.
Use num_chans read from VBIOS to determine the available MALL size we can use

[How]
Define max_chans for DCN32 and DCN321.
If num_chans is max_chans, then return max_chans as we can access the
 entire MALL space.
Otherwise, define avail_chans as the number of available channels we are
 allowed instead.
Return corresponding number of channels back and use this to calculate
 available MALL size.

Reviewed-by: Nevenko Stupar <Nevenko.Stupar@amd.com>
Acked-by: Alan Liu <HaoPing.Liu@amd.com>
Signed-off-by: Samson Tam <Samson.Tam@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>