rockchip: roc-rk3399-pc: Set LED only during POR and pwr_key=y

rockchip: roc-rk3399-pc: Set LED only during POR and pwr_key=y

ROC-RK3399-PC has specific set of configurations for
on-board led setup.

Due to easiness for user to know the state of the board
roc-rk339-pc board code will setup the low power led
on/off, and waiting for user to press power key and then
glow full power led.

All this needs to happen only during power-on-reset not
for soft reset or WDT.

Also, it is not a proper usage to ask the user to press
the Power key if the board connected remotely, so add
the environment variable 'pwr_key' to check as well.

So, user need to press Power key only
- during POR
- pwr_key=y

Tested-by: Suniel Mahesh <sunil@amarulasolutions.com>
Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>