ARM: dts: sun9i: Include SDC2_RST pin in mmc2_8bit_pins

mmc2_8bit_pins is used with eMMC chips, which also have a reset pin.
The MMC controller also has a reset output that is supported.

Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>