ARM: dts: sun8i: r40: Add node for system controller

Allwinner R40 has system controller and SRAM C1 region similar to that
in A10.

Add nodes for them.

Signed-off-by: Jernej Skrabec <jernej.skrabec@siol.net>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://lore.kernel.org/r/20200825173523.1289379-3-jernej.skrabec@siol.net