drm/amdgpu: mention RDNA support in docu

The amdgpu kernel module has supported RDNA for a while,
mention that in the module description.

v2: Add CDNA as well (Alex)
Signed-off-by: Peter Maucher <bellosilicio@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

Documentation/gpu/amdgpu/index.rst

@@ -3,7 +3,7 @@
 ==========================
 
 The drm/amdgpu driver supports all AMD Radeon GPUs based on the Graphics Core
-Next (GCN) architecture.
+Next (GCN), Radeon DNA (RDNA), and Compute DNA (CDNA) architectures.
 
 .. toctree::