drm/amd/display: get_atomic_property missing for drm_connector_funcs

DRM_IOCTL_MODE_GETCONNECTOR fails with EINVAL on enabling DRIVER_ATOMIC
With this DRM_IOCTL_MODE_GETCONNECTOR returns all the connector properties.
freesync_property and freesync_capable_property return 0 currently.

TESTS(On Chromium OS on Stoney Only)
* Builds without compilation errors.
* 'atomictest' proceeds after applying patch and fails with vblank event
timed out.
* Chromium OS ui comes up.

Signed-off-by: Pratik Vishwakarma <Pratik.Vishwakarma@amd.com>
Reviewed-by: Tony Cheng <Tony.Cheng@amd.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>