ARM: dts: aspeed: rainier: Add power-config-full-load gpio

ARM: dts: aspeed: rainier: Add power-config-full-load gpio

Add the power-config-full-load described in:
https://github.com/openbmc/docs/blob/master/designs/device-tree-gpio-naming.md#power-config-full-load

The power-config-full-load gpio is designed to be used to specify how
many power supplies the system should have, in rainier it is 2 or 4.  If
enough power supplies fail so that the system no longer has redundancy
(no longer n+1), the hardware will signal to the Onboard Chip Controller
that the system may be oversubscribed, and performance may need to be
reduced so the system can maintain it's powered on state.

Signed-off-by: Adriana Kobylak <anoo@us.ibm.com>
Reviewed-by: Eddie James <eajames@linux.ibm.com>
Link: https://lore.kernel.org/r/20211005192226.213539-1-anoo@linux.ibm.com
Signed-off-by: Joel Stanley <joel@jms.id.au>