Rename vm_create() to vm_create_barebones() and drop the @phys_pages
param.  Pass '0' for the number of pages even though some callers pass
'DEFAULT_GUEST_PHY_PAGES', as the intent behind creating truly barebones
VMs is purely to create a VM, i.e. there aren't vCPUs, there's no guest
code loaded, etc..., and so there is nothing that will ever need or
consume guest memory.

Freeing up the name vm_create() will allow using the name for an inner
helper to the other VM creators, which need a "full" VM.

Opportunisticaly rewrite the function comment for addr_gpa2alias() to
focus on what the _function_ does, not what its _sole caller_ does.
Signed-off-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>