drm/amd/display: Fetch Mall caps from DC

[Why]
When performing P-State switching with Subvp on 8k (downscaled to 4k).
corruption can be seen on the screen. MALL data was not being fetched
from DC, and the system things there is more MALL space then what is
actually available.

[How]
Read MALL size from dc caps.

Reviewed-by: Dillon Varone <dillon.varone@amd.com>
Acked-by: Zaeem Mohamed <zaeem.mohamed@amd.com>
Signed-off-by: Daniel Sa <daniel.sa@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>