dt-bindings: pinctrl: mt8195: change pull up/down description

For supporting SI units in "bias-pull-down" & "bias-pull-up",
change pull up/down description
and add "mediatek,rsel_resistance_in_si_unit" description.

Signed-off-by: Zhiyong Tao <zhiyong.tao@mediatek.com>
Link: https://lore.kernel.org/r/20210924080632.28410-3-zhiyong.tao@mediatek.com


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