drm/amdgpu: Rename amdgpu_display_framebuffer_domains()

It returns supported domains for display, and domains actually used are to be
decided later when pinned.

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