pinctrl: mt7986: allow configuring uart rx/tx and rts/cts separately

Some mt7986 boards use uart rts/cts pins as gpio,
This patch allows to change rts/cts to gpio mode, but keep
rx/tx as UART function.

Signed-off-by: Frank Wunderlich <frank-w@public-files.de>
Signed-off-by: Sam Shih <sam.shih@mediatek.com>
Link: https://lore.kernel.org/r/20221008164807.113590-1-linux@fw-web.de


Signed-off-by: Linus Walleij <linus.walleij@linaro.org>