Process the flags (by calling _busdma_flags), after we did some
sanity checking on the arguments.
PROCDESC is no more.
Call kmem_alloc_contig() with M_NOWAIT for now. This needs to come from
the user of the busdma_mem_alloc() interface, but that needs a bit of
review.
Enable PREEMPTION by default.
Add FDESCFS, needed/used by poudriere.
Bump BUS_SPACE_MAXADDR from 2^31-1 to 2^64-1. The bus_dma compat layer
panics, because it checks that the maximum address passed to
bus_dma_tag_create() matches BUS_SPACE_MAXADDR and finds that it doesn't
for psycho(4). The psycho(4) driver passes ~0 and not BUS_SPACE_MAXADDR.
sparc64 is a 64-bit archirecture, so why isn't BUS_SPACE_MAXADDR 2^61-1?

I'm probably groing to regret this change, but so far it doesn't look
like it's having any negative side-effects.

While here, postfix U and UL to the BUS_SPACE constants.
Add support for switching sparc64 to busdma/mi. The legacy bus_dma
bits are conditionally compiled based on LEGACY_BUS_DMA option.
Put maxaddr in the panic string. It's helpful.