vmm: Harmonize compat ioctl definitions

For compat ioctls and structures, we use a mix of suffixes: _old,
_fbsd<version>, _<version>. Standardize on _<version> to make things
more consistent. No functional change intended.

Reported by: jhb
Reviewed by: corvink, jhb
Differential Revision: https://reviews.freebsd.org/D46449