dt-bindings: pinctrl: mediatek: mt7622: add "antsel" function

MT7622 pinctrl has ANTSEL* pins. Linux support for those was added in
the commit 19f599e8 ("pinctrl: mediatek: mt7622: add antsel
pins/groups"). Include them in binding.

Cc: Chuanhong Guo <gch981213@gmail.com>
Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Acked-by: Rob Herring <robh@kernel.org>
Message-ID: <20240423045502.7778-2-zajec5@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>