ARM: dts: aspeed: everest: Add system level indicator leds

These are the system level indicator leds that are driven by
PCA9551 connected to the Operator Panel.

Signed-off-by: Vishwanatha Subbanna <vishwa@linux.vnet.ibm.com>
Signed-off-by: Joel Stanley <joel@jms.id.au>
Link: https://lore.kernel.org/r/20210607031259.475020-2-joel@jms.id.au