bhyve: simplify memory assignment to VMs

[Neel Natu]

Hi,

I am going to commit a change soon that simplifies how memory is
assigned to a VM from a command line perspective.

At the moment if you want to create a VM with say 8GB of memory you
need to express this as "-m 2048 -M 6144" or "-m 1024 -M 7168" or some
split that adds up to 8192MB. This is very flexible but is also very
confusing to most users who don't know or care about the location of
the PCI hole.

I am going to change this so that the memory size is specified
entirely with the "-m <memsize>" option and the "-M" option will
disappear altogether.

Of course, this means that scripts using "-M" will break and hence
this heads up.

I did consider making this a backward compatible change but given the
stage of development of bhyve it seemed early to start accumulating
compatibility crud.

best
Neel