rockchip: show boot stages on nanopi R6 system LED

rockchip: show boot stages on nanopi R6 system LED

Set up openwrt to show boot progress on the nanopi R6S or R6C system LED.

The LED blinking states indicate the boot stage. The LED is defined as
a power LED, but can still be set to heartbeat in /etc/config/system
after the system is done booting.

Signed-off-by: Michel Lespinasse <michel@lespinasse.org>
Link: https://github.com/openwrt/openwrt/pull/17638
(cherry picked from commit de9ad11dac094b6074c9b23341acbc28806404ae)
Link: https://github.com/openwrt/openwrt/pull/18347
Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>