mx6: soc: Move mxs_dma_init() into the mxs nand driver

Currently the following build error is seen when a board using MMC SPL
is built and the MXS nand driver is also selected:

arch/arm/cpu/armv7/built-in.o: In function `arch_cpu_init':
arch/arm/cpu/armv7/mx6/soc.c:432: undefined reference to 'mxs_dma_init'

On mx6 the only user of mxs_dma_init() is the mxs nand driver, so
move it there.

Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>

arch/arm/cpu/armv7/mx6/soc.c

@@ -427,11 +427,6 @@ int arch_cpu_init(void)
 
 	imx_set_wdog_powerdown(false); /* Disable PDE bit of WMCR register */
 
-#ifdef CONFIG_APBH_DMA
-	/* Start APBH DMA */
-	mxs_dma_init();
-#endif
-
 	init_src();
 
 	return 0;