Use asm-generic/dma-mapping-common.h to handle all DMA mapping operations
and establish a default get_dma_ops() that forwards all operations to the
existing code.
Augment dev_archdata to carry a pointer to the struct dma_map_ops, allowing
DMA operations to be overridden on a per device basis. Currently this is
never filled in, so the default dma_map_ops are used. A follow-on patch
sets this for Octeon PCI devices.
Also initialize the dma_debug system as it is now used if it is configured.
Includes fixes by Kevin Cernekee <cernekee@gmail.com>.