drm: meson_drv add shutdown function

Problem: random stucks on reboot stage about 1/20 stuck/reboots
// debug kernel log
[    4.496660] reboot: kernel restart prepare CMD:(null)
[    4.498114] meson_ee_pwrc c883c000.system-controller:power-controller: shutdown begin
[    4.503949] meson_ee_pwrc c883c000.system-controller:power-controller: shutdown domain 0:VPU...
...STUCK...

Solution: add shutdown function to meson_drm driver
// debug kernel log
[    5.231896] reboot: kernel restart prepare CMD:(null)
[    5.246135] [drm:meson_drv_shutdown]
...
[    5.259271] meson_ee_pwrc c883c000.system-controller:power-controller: shutdown begin
[    5.274688] meson_ee_pwrc c883c000.system-controller:power-controller: shutdown domain 0:VPU...
[    5.338331] reboot: Restarting system
[    5.358293] psci: PSCI_0_2_FN_SYSTEM_RESET reboot_mode:0 cmd:(null)
bl31 reboot reason: 0xd
bl31 reboot reason: 0x0
system cmd  1.
...REBOOT...

Tested: on VIM1 VIM2 VIM3 VIM3L khadas sbcs - 1000+ successful reboots
and Odroid boards, WeTek Play2 (GXBB)

Fixes: bbbe775e ("drm: Add support for Amlogic Meson Graphic Controller")
Signed-off-by: Artem Lapkin <art@khadas.com>
Tested-by: Christian Hewitt <christianshewitt@gmail.com>
Acked-by: Neil Armstrong <narmstrong@baylibre.com>
Acked-by: Kevin Hilman <khilman@baylibre.com>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210302042202.3728113-1-art@khadas.comSigned-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>

drivers/gpu/drm/meson/meson_drv.c

@@ -482,6 +482,16 @@ static int meson_probe_remote(struct platform_device *pdev,
 	return count;
 }
 
+static void meson_drv_shutdown(struct platform_device *pdev)
+{
+	struct meson_drm *priv = dev_get_drvdata(&pdev->dev);
+	struct drm_device *drm = priv->drm;
+
+	DRM_DEBUG_DRIVER("\n");
+	drm_kms_helper_poll_fini(drm);
+	drm_atomic_helper_shutdown(drm);
+}
+
 static int meson_drv_probe(struct platform_device *pdev)
 {
 	struct component_match *match = NULL;
@@ -553,6 +563,7 @@ static const struct dev_pm_ops meson_drv_pm_ops = {
 
 static struct platform_driver meson_drm_platform_driver = {
 	.probe      = meson_drv_probe,
+	.shutdown   = meson_drv_shutdown,
 	.driver     = {
 		.name	= "meson-drm",
 		.of_match_table = dt_match,