drm/amd/display: Fix gpio port mapping issue

[Why]
1. Port of gpio has different mapping.

[How]
1. Add a dummy entry in mapping table.
2. Fix incorrect mask bit field access.

Reviewed-by: Alvin Lee <Alvin.Lee2@amd.com>
Acked-by: Alan Liu <HaoPing.Liu@amd.com>
Signed-off-by: Steve Su <steve.su@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>