dt-bindings: leds: Add disk write/read and usb-host/usb-gadget

The triggers enum misses 3 cases used by gemini DT.
usb-host was added via commit 0cfbd328 ("usb: Add LED triggers for USB activity")
so we add also as valid trigger usb-gadget which was added along in this
commit.

disk-read/disk-write were added by commit d1ed7c55 ("leds: Extends disk trigger for reads and writes")
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Rob Herring <robh@kernel.org>

Signed-off-by: Corentin Labbe <clabbe@baylibre.com>
Signed-off-by: Lee Jones <lee@kernel.org>
Link: https://lore.kernel.org/r/20230131140304.626779-1-clabbe@baylibre.com