drm/amdgpu/vg20:increase 3 rings for AMDGPU_MAX_RINGS

For Vega20, there are two UVD Hardware. One more UVD hardware
adds one decode ring and two encode rings. So AMDGPU_MAX_RINGS
need increase by 3.

Signed-off-by: James Zhu <James.Zhu@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/amdgpu_ring.h

@@ -29,7 +29,7 @@
 #include <drm/drm_print.h>
 
 /* max number of rings */
-#define AMDGPU_MAX_RINGS		18
+#define AMDGPU_MAX_RINGS		21
 #define AMDGPU_MAX_GFX_RINGS		1
 #define AMDGPU_MAX_COMPUTE_RINGS	8
 #define AMDGPU_MAX_VCE_RINGS		3