Fixes the following W=1 kernel build warning(s):

 drivers/gpu/drm/amd/amdgpu/../display/dc/gpio/gpio_service.c: In function ‘dal_gpio_service_create’:
 drivers/gpu/drm/amd/amdgpu/../display/dc/gpio/gpio_service.c:71:4: warning: implicit conversion from ‘enum dce_version’ to ‘enum dce_environment’ [-Wenum-conversion]
 drivers/gpu/drm/amd/amdgpu/../display/dc/gpio/gpio_service.c:77:4: warning: implicit conversion from ‘enum dce_version’ to ‘enum dce_environment’ [-Wenum-conversion]

Cc: Harry Wentland <harry.wentland@amd.com>
Cc: Leo Li <sunpeng.li@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: "Christian König" <christian.koenig@amd.com>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: amd-gfx@lists.freedesktop.org
Cc: dri-devel@lists.freedesktop.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

[Why]
Implementation of stereo mux register is complete, but unused. Need to
call functions to write relevant configs.

[How]
Add function to write stereo config for enable/disable case and call in
stereo control interface.

Signed-off-by: Murton Liu <murton.liu@amd.com>
Reviewed-by: Aric Cyr <Aric.Cyr@amd.com>
Acked-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

Supported DCE versions: 8.0, 10.0, 11.0, 11.2

v2: rebase against 4.11

Signed-off-by: Harry Wentland <harry.wentland@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>