drm/radeon: fix bank tiling parameters on SI

The sixteen bank case wasn't handled here, leading to GPU
crashes because of userspace miscalculation.
Signed-off-by: NChristian König <deathsimple@vodafone.de>
Cc: stable@vger.kernel.org
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/radeon/si.c

@@ -1640,10 +1640,18 @@ static void si_gpu_init(struct radeon_device *rdev)
 		rdev->config.si.tile_config |= (3 << 0);
 		break;
 	}	
-	if ((mc_arb_ramcfg & NOOFBANK_MASK) >> NOOFBANK_SHIFT)
-		rdev->config.si.tile_config |= 1 << 4;
-	else
+	switch ((mc_arb_ramcfg & NOOFBANK_MASK) >> NOOFBANK_SHIFT) {
+	case 0: /* four banks */
 		rdev->config.si.tile_config |= 0 << 4;
+		break;
+	case 1: /* eight banks */
+		rdev->config.si.tile_config |= 1 << 4;
+		break;
+	case 2: /* sixteen banks */
+	default:
+		rdev->config.si.tile_config |= 2 << 4;
+		break;
+	}
 	rdev->config.si.tile_config |=
 		((gb_addr_config & PIPE_INTERLEAVE_SIZE_MASK) >> PIPE_INTERLEAVE_SIZE_SHIFT) << 8;
 	rdev->config.si.tile_config |=