dmaengine: split out virtual channel DMA support from sa11x0 driver

Split the virtual slave channel DMA support from the sa11x0 driver so
this code can be shared with other slave DMA engine drivers.

Acked-by: Linus Walleij <linus.walleij@linaro.org>
Tested-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
diff --git a/drivers/dma/Kconfig b/drivers/dma/Kconfig
index aadeb5b..eb2b60e 100644
--- a/drivers/dma/Kconfig
+++ b/drivers/dma/Kconfig
@@ -255,6 +255,7 @@
 	tristate "SA-11x0 DMA support"
 	depends on ARCH_SA1100
 	select DMA_ENGINE
+	select DMA_VIRTUAL_CHANNELS
 	help
 	  Support the DMA engine found on Intel StrongARM SA-1100 and
 	  SA-1110 SoCs.  This DMA engine can only be used with on-chip
@@ -263,6 +264,9 @@
 config DMA_ENGINE
 	bool
 
+config DMA_VIRTUAL_CHANNELS
+	tristate
+
 comment "DMA Clients"
 	depends on DMA_ENGINE