drm/rockchip: vop: set vop enabled after enable iommu

there is a Bug that:
  vop_enable()->drm_vblank_on, drm_vblank_on may call vop
enable vblank. if it happen, vblank enable would failed,
then cause irq status error. because is_enabled value is set
after drm_vblank_on.

after enable vop clocks and iommu regs, we can sure that
R/W vop regs and do vop plane flip is safe, so place
is_enabled = true after enable iommu is suitable.
Signed-off-by: Mark Yao <mark.yao@rock-chips.com>

drivers/gpu/drm/rockchip/rockchip_drm_vop.c

@@ -420,6 +420,11 @@ static void vop_enable(struct drm_crtc *crtc)
 		goto err_disable_aclk;
 	}
 
+	/*
+	 * At here, vop clock & iommu is enable, R/W vop regs would be safe.
+	 */
+	vop->is_enabled = true;
+
 	spin_lock(&vop->reg_lock);
 
 	VOP_CTRL_SET(vop, standby, 0);
@@ -430,8 +435,6 @@ static void vop_enable(struct drm_crtc *crtc)
 
 	drm_vblank_on(vop->drm_dev, vop->pipe);
 
-	vop->is_enabled = true;
-
 	return;
 
 err_disable_aclk:
@@ -462,6 +465,8 @@ static void vop_disable(struct drm_crtc *crtc)
 	VOP_CTRL_SET(vop, standby, 1);
 
 	spin_unlock(&vop->reg_lock);
+
+	vop->is_enabled = false;
 	/*
 	 * disable dclk to stop frame scan, so we can safely detach iommu,
 	 */
@@ -471,8 +476,6 @@ static void vop_disable(struct drm_crtc *crtc)
 
 	clk_disable(vop->aclk);
 	clk_disable(vop->hclk);
-
-	vop->is_enabled = false;
 }
 
 /*