pinctrl: uniphier: remove eMMC hardware reset pin-mux

This is handled by the mmc-pwrseq-emmc driver, which controls
an eMMC hardware reset via a GPIO line.

Remove it from the function pin-mux settings.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>