MFD: mcp-sa11x0: remove DMA initializers and variables

The dma_device_t variables are only ever written to by mcp-sa11x0 and
never read.  As the old SA11x0 DMA support will be removed, remove
these so that it no longer depends on the old SA11x0 DMA definitions.

Acked-by: Jochen Friedrich <jochen@scram.de>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>