Allow the CPU code, and any board specific initialisation
code to change the allocation order of the DMA channels,
or stop a peripheral allocating any DMA at-all.

This is due to the scarce mapping of DMA channels on
some earlier S3C24XX cpus, where the selection changes
depending on the channel in use.
Signed-off-by: Ben Dooks <ben-linux@fluff.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>