drm/radeon: add new SI pci id

commit 0181bd5dea2ed0696f84591a92da0b6a1f1a2e62 upstream.

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>