drm/amd: Add dce-12.1 gpio aux registers (v2)

Updating dce12 register headers by adding dc registers
required for potential DP LTTPR support.

v2: fix mode change

Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Roman Li <Roman.Li@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>