ARM: dts: sun5i: Provide default muxing for relevant controllers

The I2C's, MMC0 and MMC1 controllers have only one muxing option in the
SoC. In such a case, we can just move the muxing into the DTSI, and remove
it from the DTS.

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