ARM: Allow SoCs to enable scatterlist chaining

Allow SoCs to enable the scatterlist chaining support, which allows
scatterlist tables to be broken up into smaller allocations.

As support for this feature depends on the implementation details of
the users of the scatterlists, we can't enable this globally without
auditing all the users, which is a very big task.  Instead, let SoCs
progressively switch over to using this.

SoC drivers using scatterlists and SoC DMA implementations need
auditing before this option can be enabled for the SoC.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
(cherry picked from commit 9b676aa0ecf52b3ce9abb9eb6556273748e970cf)