libvmmapi: Split the ioctl list into MI and MD lists

To enable use in capability mode, libvmmapi needs a list of all the
ioctls that might be invoked on the vmm device handle. Some of these
ioctls are amd64-specific. Move the ioctl list to vmmapi_machdep.c and
define a list of MI ioctls so that the arm64 port can build its own list
without duplicating common ioctls. No functional change intended.

Reviewed by: corvink, jhb
MFC after: 2 weeks
Sponsored by: Innovate UK
Differential Revision: https://reviews.freebsd.org/D41001