arm64: dts: allwinner: Fix pinctrl node names

Some pinctrl node names for the A64 and H6 do not follow the convention
that we switched to and enforced, most notably by using underscores in node
names, which also trigger a DTC warning.

Let's change that.

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