ARM: dts: sun4i: Switch to new system control compatible string

This switches the sun4i-a10 dtsi to use the new compatible for the
system-control block (previously named SRAM controller) instead of
the deprecated one.

The node name is also updated to reflect the fact that the controller
described is really about system control rather than SRAM control.

Signed-off-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
[Maxime: Amended the commit message]
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>