dt-bindings: sram: sunxi: Introduce new A10 binding for system-control

Following-up on the introduction of a new binding for the A64, this
introduces a system-control binding for the A10 as a replacement of
the sram-controller binding.

This change is motivated by consistency with the Allwinner literature,
that mentions system control over SRAM controller. Moreover, the system
control block is sometimes used for more than SRAM (e.g. for muxing
related to the ethernet PHY).

Signed-off-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>