[ARM] Orion: LED support for HP mv2120

The HP mv2120 has several LEDs that are controlled through gpio.
Export the health LED, the red SATA LEDs as well as two gpios
that control the brightness of _all_ LEDs to userland.  The
Ethernet and power LEDs can't be controlled through gpio and the
blue SATA LEDs are handled via the SATA driver.

Signed-off-by: Martin Michlmayr <tbm@cyrius.com>
Signed-off-by: Nicolas Pitre <nico@marvell.com>