Add prefixes to method structures member names. No functional change.
Remove the lbl argument from usbd_{bulk,intr}_transfer.
Whitespace.
Step #1 of memory allocation re-organisation.

Centralised the buffer allocation routine which now supports DMA
and non-DMA capable host controllers.  Remove the
ubm_{alloc,free}m methods from usbd_bus_methods.

The buffer allocation is only allowed in thread context and,
therefore, negates the usefulness of the reserve dma code which
is removed in this change.

USBD_NO_COPY is also no longer required as usbd_transfer and
usbd_transfer_complete now track buffer usage and handle any
copying.