ARM: dts: aspeed: everest: Add pcie slot indicator leds

These are pcie slot indicator leds driven by PCA9552.

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/20210607031259.475020-4-joel@jms.id.au