busdma: Add PRIVBZONE and ALLOCALL bus_dma_tag_create() flags.

busdma: Add PRIVBZONE and ALLOCALL bus_dma_tag_create() flags.

PRIVBZONE
  Use a private bounce zone instead of a shared one.  A private bounce
  zone will vanish if the dma_tag is destroyed.

ALLOCALL
  Allocate all required resources (mainly bounce buffer), if any
  allocation failes, bus_dmamap_create() will fail.

Using PRIVBZONE alone could possiblely reduce the contention between
driver instances.

Using PRIVBZONE and ALLOCALL could promise that the "defered dmamap
load callback" will not happen.  This could be used to ease some driver
work and reduce the work load to fix the existing drivers which may
(incorrectly) rely on or may not expect the "defered dmamap load
callback" semantic of bus_dmamap_load().