ARM: moxart: move DMA_OF selection to driver

Move the DMA_OF selection to the DMA driver to fix kconfig warning:

warning: (ARCH_MOXART) selects DMA_OF which has unmet direct dependencies (DMADEVICES && OF)

Signed-off-by: Rob Herring <robh@kernel.org>
Signed-off-by: Olof Johansson <olof@lixom.net>
diff --git a/drivers/dma/Kconfig b/drivers/dma/Kconfig
index 9bed1a2..605b016 100644
--- a/drivers/dma/Kconfig
+++ b/drivers/dma/Kconfig
@@ -346,6 +346,7 @@
 	tristate "MOXART DMA support"
 	depends on ARCH_MOXART
 	select DMA_ENGINE
+	select DMA_OF
 	select DMA_VIRTUAL_CHANNELS
 	help
 	  Enable support for the MOXA ART SoC DMA controller.