MIPS: Always select ARCH_HAS_SYNC_DMA_FOR_CPU for noncoherent platforms

As now we are telling the necessity of post DMA flush per CPU type,
there is no need to select ARCH_HAS_SYNC_DMA_FOR_CPU on per platform
bias, just select it unconditionally and we can sort it at runtime.

Signed-off-by: Jiaxun Yang <jiaxun.yang@flygoat.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>