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>

arch/arm/mach-moxart/Kconfig

@@ -2,7 +2,6 @@ config ARCH_MOXART
 	bool "MOXA ART SoC" if ARCH_MULTI_V4T
 	select CPU_FA526
 	select ARM_DMA_MEM_BUFFERABLE
-	select DMA_OF
 	select USE_OF
 	select CLKSRC_OF
 	select CLKSRC_MMIO

drivers/dma/Kconfig

@@ -346,6 +346,7 @@ config MOXART_DMA
 	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.