o add support to byte swap EHCI descriptor contents; the IXP435
has dual-EHCI controllers integral but descriptor contents are
in big-endian format; this support is configured with the
USB_EHCI_BIG_ENDIAN_DESC option and enabled with EHCI_SCFLG_BIGEDESC
o clean up EHCI USBMODE register setup during init; add #defines for
bit values
o split debug support out into a new file and enable use through ddb
o while here remove a bunch of lingering netbsd-isms
Reviewed by: imp
65fa43968e