mvebu: fix LEDs on Fortinet FortiGate devices

mvebu: fix LEDs on Fortinet FortiGate devices

On Fortinet FortiGate 30E/50E, some multiple LEDs have no "function"
property and only "color" property is available for the new binding of
LED on Linux Kernel.
9d93b6d091 ("mvebu: drop redundant label with new LED color/function
format") removes "label" property from LEDs, then, multiple "<color>:"
(ex.: "green:"/"red:"/"amber:") will be appeared as LED names and
renamed to "<color>:_<num>" (ex.: "green:_1", "green:_2", ...) by
kernel.

log:

[   12.425170] leds-gpio gpio-leds: Led green: renamed to green:_1 due to name collision
[   12.520390] leds-gpio gpio-leds: Led amber: renamed to amber:_1 due to name collision
[   12.614931] leds-gpio gpio-leds: Led green: renamed to green:_2 due to name collision
[   12.709895] leds-gpio gpio-leds: Led green: renamed to green:_3 due to name collision
[   12.804439] leds-gpio gpio-leds: Led amber: renamed to amber:_2 due to name collision
[   12.898969] leds-gpio gpio-leds: Led green: renamed to green:_4 due to name collision
[   12.993504] leds-gpio gpio-leds: Led amber: renamed to amber:_3 due to name collision
[   13.088033] leds-gpio gpio-leds: Led green: renamed to green:_5 due to name collision
[   13.182570] leds-gpio gpio-leds: Led green: renamed to green:_6 due to name collision
[   13.277103] leds-gpio gpio-leds: Led amber: renamed to amber:_4 due to name collision
[   13.371636] leds-gpio gpio-leds: Led green: renamed to green:_7 due to name collision

/sys/class/leds:

root@OpenWrt:/# ls /sys/class/leds/
amber:        amber:_4      green:_2      green:_6      red:alarm
amber:_1      amber:alarm   green:_3      green:_7      red:status
amber:_2      green:        green:_4      green:status
amber:_3      green:_1      green:_5      red:

Fix this issue by adding missing "function" (and "function-enumerator")
property those to LEDs on Fortinet FortiGate devices.
Note: there is no appropriate function for "ha" LEDs in
dt-bindings/leds/common.h, so use the hardcoded string for them instead.

Fixes: 9d93b6d091 ("mvebu: drop redundant label with new LED color/function format")
Signed-off-by: INAGAKI Hiroshi <musashino.open@gmail.com>