dt-bindings: leds: Add generic LED consumer documentation

dt-bindings: leds: Add generic LED consumer documentation

Introduce common generic led consumer binding, where consumer defines
led(s) by phandle, as opposed to trigger-source binding where the
trigger source is defined in led itself.

Add already used in some schemas 'leds' parameter which expects
phandle-array. Additionally, introduce 'led-names' which could be used
by consumers to map LED devices to their respective functions.

Signed-off-by: Aleksandrs Vinarskis <alex@vinarskis.com>
Reviewed-by: "Rob Herring (Arm)" <robh@kernel.org>
Link: https://lore.kernel.org/r/20250910-leds-v5-1-bb90a0f897d5@vinarskis.com
Signed-off-by: Lee Jones <lee@kernel.org>