dmaengine: Kconfig: Extend the dependency for MXS_DMA

Currently it is not possible to select the mxs dma driver when only
mx6sx or mx7 are selected.

Extend the dependency to allow the mxs dma driver to be built whenever
ARCH_MXS or ARCH_MXC is selected.

This has the benefit to avoid having to add new entries in the
MXS_DMA Kconfig everytime a new i.MX SoC shows up and it also makes
it consistent with the other i.MX DMA engines, such as IMX_DMA and
IMX_SDMA.

While at it, also pass COMPILE_TEST for increasing the build coverage.

Acked-by: Stefan Agner <stefan@agner.ch>
Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>