of: dma: Make of_dma_deconfigure() public

As part of moving DMA initializing to probe time the
of_dma_deconfigure() function will need to be called from different
source files. Make it public and move it to drivers/of/device.c where
the of_dma_configure() function is.

Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>