kernel: ar8327: support LED device tree bindings

kernel: ar8327: support LED device tree bindings

The ar8216 switch driver supports exposing configuration of AR8327 and
AR8337 switch LEDs to the userspace, however it is only configurable
through platform data, causing the devices ported from ar71xx target to
lack the support.
Since there is still a long way to go until we can migrate the target to
qca8k, an interim solution is needed.
Extend ar8327_hw_config_of function to parse a "leds"
subnode, which will populate the missing platform data based on device
tree contents, and restore the existing support for the LEDs.
Standard bindings apply, mapping "reg" property to LED index, with
addition of "qca,led-mode" property, which selects HW (0) or SW (1)
mode, defaulting to HW mode.

Signed-off-by: Lech Perczak <[email protected]>
Link: https://github.com/openwrt/openwrt/pull/12487
Signed-off-by: Hauke Mehrtens <[email protected]>