ARM: imx: gpmi-nand depends on mxs-dma

It is not currently possible to build the gpmi-nand driver without
also building the mxs-dma driver. Clarify this Kconfig and enable
both in the defconfig file so we can build it again with both enabled.

drivers/built-in.o: In function `gpmi_dma_filter':
clk-fixed-factor.c:(.text+0xafc18): undefined reference to `mxs_dma_is_apbh'
make[1]: *** [vmlinux] Error 1
make: *** [sub-make] Error 2

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Dirk Behme <dirk.behme@de.bosch.com>
Cc: Shawn Guo <shawn.guo@linaro.org>
Cc: Sascha Hauer <kernel@pengutronix.de>