MIPS: bmips: Remove obsolete DMA mapping support

The code in 'arch/mips/bmips/dma.c' performed DMA mapping for inbound
regions.  This mapping was and is required for the Broadcom STB PCIe
controller HW.  This code is removed as the current 'struct device' has a
@dma_range_map field which performs the same functionality by processing
the "dma-ranges" DT property.

Subsequently, ARCH_HAS_PHYS_TO_DMA is now unset since the dma_to_phys()
and phys_to_dma() functions are removed.

Signed-off-by: Jim Quinlan <jim2101024@gmail.com>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>