hmp: gpa2hva and gpa2hpa hostaddr command

These commands are useful when testing machine-check passthrough.
gpa2hva is useful to inject a MADV_HWPOISON madvise from gdb, while
gpa2hpa is useful to inject an error with the mce-inject kernel
module.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <1490021158-4469-1-git-send-email-pbonzini@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20170420133058.12911-1-pbonzini@redhat.com>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
