drm/amd/display: Populate hostvm parameter before DML calculation

[Why]
If the system does not have hostvm enabled, disabling it for
DML validation will allow more modes to pass at lower voltage
levels.

[How]
When initializing HostVM save state to hubbub and read back
when populating DML pipes from context.

Signed-off-by: Sung Lee <sung.lee@amd.com>
Acked-by: Bindu Ramamurthy <bindu.r@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>