drm: meson_drv add shutdown function

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: bbbe775ec5b5 ("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.com
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>