The dma_mask and coherent_dma_mask need to be set or DMA memory allocations
will fail with error messages like this:

  ep93xx-dma ep93xx-dma-m2p: coherent DMA mask is unset

  ep93xx-dma ep93xx-dma-m2m: coherent DMA mask is unset

Add the missing information to the ep93xx-dma-m2p and ep93xx-dma-m2m
devices.
Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Reported-by: Jeremy Moles <cubicool@gmail.com>
Tested-by: Alexander Sverdlin <subaparts@yandex.ru>
Cc: Ryan Mallon <rmallon@gmail.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>