Since r296250 it is no longer possible for devices to use bus space

Since r296250 it is no longer possible for devices to use bus space
addresses exceeding 32 bit, so bump BUS_SPACE_MAXADDR to 64 bit.
The whole situation is sub par, though; prior to r296250 and despite
what their names imply, BUS_SPACE_MAX* were primarily, even almost
exclusively used for bus_dma(9). Now these macros also have a vital
role for bus_space(9). However, it does not necessarily hold that
both bus DMA and space addresses universally have the same limits
per platform.
As for sparc64, 64 bit clearly is beyond what can be addressed via
the various IOMMUs. With this change in place, we now rely on the
parent bus DMA tags of the host-to-foo drivers causing the child
tags to be capped as necessary.

PR:		207998