drm/amd/display: use configurable FBC option in dm

Replace ENABLE_FBC macro with config option CONFIG_DRM_AMD_DC_FBC
in dm. DC code has been already updated the same way.

Signed-off-by: Roman Li <Roman.Li@amd.com>
Reviewed-by: Shirish Shankarappa <Shirish.S@amd.com>
Acked-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>