ARM: mvebu: Add RN104 SATA LEDs driven via NXP PCA9554 I2C to GPIO muxer

NETGEAR ReadyNAS 104 has a NXP PCA9554 I2C to GPIO chip. Among the 8 GPIO
lines the chip makes available, four are used on the device to control
the SATA LEDs (the four remaining ones are used for SATA disk presence).
This patch adds DT entries for NXP PCA9554 and the four SATA GPIO LEDs.

Signed-off-by: Arnaud Ebalard <arno@natisbad.org>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>