drm/radeon/si: Add support for CP DMA to CS checker for compute v2

Also add a new RADEON_INFO query to check that CP DMA packets are
supported on the compute ring.

CP DMA has been supported since the 3.8 kernel, but due to an oversight
we forgot to teach the CS checker that the CP DMA packet was legal for
the compute ring on Southern Islands GPUs.

This patch fixes a bug where the radeon driver will incorrectly reject a legal
CP DMA packet from user space.  I would like to have the patch
backported to stable so that we don't have to require Mesa users to use a
bleeding edge kernel in order to take advantage of this feature which
is already present in the stable kernels (3.8 and newer).

v2:
  - Don't bump kms version, so this patch can be backported to stable
    kernels.

Cc: stable@vger.kernel.org
Signed-off-by: Tom Stellard <thomas.stellard@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/radeon/radeon_kms.c

@@ -433,6 +433,9 @@ int radeon_info_ioctl(struct drm_device *dev, void *data, struct drm_file *filp)
 			return -EINVAL;
 		}
 		break;
+	case RADEON_INFO_SI_CP_DMA_COMPUTE:
+		*value = 1;
+		break;
 	default:
 		DRM_DEBUG_KMS("Invalid request %d\n", info->request);
 		return -EINVAL;