drm/amd/display: Add DCN315 GPIO

Add GPIO interfaces for DCN 3.1.5.

Signed-off-by: Qingqing Zhuo <qingqing.zhuo@amd.com>
Acked-by: Harry Wentland <Harry.Wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>