vmm/vmd/vmctl: standardize memory units to bytes

vmm/vmd/vmctl: standardize memory units to bytes

At different points in the vm lifecycle vmm(4), vmctl(8), and vmd(8)
refer to a vm's memory range sizes in either bytes or megabytes.
This is needlessly complex.

Switch to using bytes everywhere and adjust types and constants
accordingly. While this makes it possible to specify vm's with
memory in fractions of megabytes, the logic requiring whole
megabyte values remains.

Feedback from deraadt@, mlarkin@, and Matthew Martin.

ok mlarkin@