MIPS: Adjust the dma-common.c platform hooks.

We add a dev parameter to plat_unmap_dma_mem(), and hooks for
plat_dma_supported() and plat_extra_sync_for_device() which should be
nop changes for all existing targets.

Signed-off-by: David Daney <ddaney@caviumnetworks.com>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>