Add new emmc groups in the pinctrl driver for the
MediaTek MT7981 SoC:
* emmc reset, with pin 15.
* emmc 4-bit bus-width, with pins 16 to 19, and 24 to 25.
* emmc 8-bit bus-width, with pins 16 to 25.

The existing emmc_45 group is kept for legacy reasons, even
if this is the union of emmc_reset and emmc_8 groups.
Signed-off-by: Jean Thomas <jean.thomas@wifirst.fr>
Reviewed-by: Daniel Golle <daniel@makrotopia.org>
Link: https://lore.kernel.org/r/20240117145547.3354242-1-jean.thomas@wifirst.frSigned-off-by: Linus Walleij <linus.walleij@linaro.org>