sunxi: Add mmc[1-3] pinmux settings for R40

The PIO is generally compatible with the A20, except that it routes the
full 8 bits and eMMC reset pins for mmc2.

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