drm/amdgpu: add Stoney chip family

Stoney is based on Carrizo with some IP upgrades.

Signed-off-by: Samuel Li <samuel.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
index 19e185e..645690b 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
@@ -57,6 +57,7 @@
 	"TONGA",
 	"FIJI",
 	"CARRIZO",
+	"STONEY",
 	"LAST",
 };