Instead of fiddling with debug_requested and vmstop_requested directly,
introduce qemu_system_debug_request and turn qemu_system_vmstop_request
into a public interface. This aligns those services with exiting ones in
vl.c.
Signed-off-by: NJan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: NMarcelo Tosatti <mtosatti@redhat.com>