drm/radeon/kms: respect single crtc cards, only create one crtc. (v2)

Also add single crtc for RN50 chips.

changes in v2:
fix vblank init to respect single crtc flag
fix r100 mode bandwidth to respect single crtc flag

Signed-off-by: Dave Airlie <airlied@redhat.com>
diff --git a/drivers/gpu/drm/radeon/radeon_display.c b/drivers/gpu/drm/radeon/radeon_display.c
index 5d8141b..44cfcfd 100644
--- a/drivers/gpu/drm/radeon/radeon_display.c
+++ b/drivers/gpu/drm/radeon/radeon_display.c
@@ -724,7 +724,11 @@
 	if (ret) {
 		return ret;
 	}
-	/* allocate crtcs - TODO single crtc */
+
+	if (rdev->flags & RADEON_SINGLE_CRTC)
+		num_crtc = 1;
+
+	/* allocate crtcs */
 	for (i = 0; i < num_crtc; i++) {
 		radeon_crtc_init(rdev->ddev, i);
 	}