pinctrl: mediatek: paris: Support generic PIN_CONFIG_DRIVE_STRENGTH_UA

Some of the MediaTek chips that utilize the Paris pinctrl driver library
support a lower drive strength (<= 1mA) than the standard drive strength
settings (2~16 mA) on certain pins. This was previously supported by the
custom MTK_PIN_CONFIG_DRV_ADV parameter along with the
"mediatek,drive-strength-adv" device tree property.

The drive strength values for this hardware are 125, 250, 500, and 1000 mA,
and can be readily described by the existing "drive-strength-microamp"
property, which then gets parsed by the generic pinconf library into the
parameter PIN_CONFIG_DRIVE_STRENGTH_UA.

Add support for PIN_CONFIG_DRIVE_STRENGTH_UA while keeping the old
custom parameter around for backward compatibility.

Signed-off-by: Chen-Yu Tsai <wenst@chromium.org>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://lore.kernel.org/r/20220308100956.2750295-9-wenst@chromium.org
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>