ARM: dts: sunxi: Rename nmi_intc to r_intc

The R_INTC block controls more than just the NMI, and it is a different
hardware block than the NMI INTC found in some other Allwinner SoCs, so
the label "nmi_intc" is inaccurate. Name it "r_intc" to match the
compatible and to match the few references in the vendor documentation.

Signed-off-by: Samuel Holland <samuel@sholland.org>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://lore.kernel.org/r/20210118055040.21910-6-samuel@sholland.org