ARM: dts: sunxi: h3/h5: add missing uart2 rts/cts pins

uart1 and uart3 had existing pin definitions for the rts/cts pairs.
Add definitions for uart2 as well.

Signed-off-by: Karl Palsson <karlp@tweak.net.au>
Acked-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>