MIPS: remove CONFIG_DMA_PERDEV_COHERENT

Just select DMA_NONCOHERENT and ARCH_HAS_SETUP_DMA_OPS from the
MIPS_GENERIC platform instead.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Huacai Chen <chenhuacai@kernel.org>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>