drm/amd/display: Parse RECEIVE_PORT0_CAP capabilities from DPCD

drm/amd/display: Parse RECEIVE_PORT0_CAP capabilities from DPCD

[Why]
DPCD register RECEIVE_PORT0_CAP contains HBlank expansion/reduction
capabilities of a DP device. These capabilities are required to enable
HBlank expansion/reduction logic.

[How]
Read raw RECEIVE_PORT0_CAP register values and store parsed fields.

Reviewed-by: Wenjing Liu <wenjing.liu@amd.com>
Signed-off-by: George Shen <george.shen@amd.com>
Signed-off-by: Roman Li <roman.li@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>