x86:monitor: control monitor.c build with CONFIG_VM_EVENT option

Replace more general CONFIG_HVM option with CONFIG_VM_EVENT which is more
relevant and specific to monitoring. This is only to clarify at build level
to which subsystem this file belongs.

No functional change here, as VM_EVENT depends on HVM.

Signed-off-by: Sergiy Kibrik <Sergiy_Kibrik@epam.com>
Acked-by: Jan Beulich <jbeulich@suse.com>

xen/arch/x86/Makefile

@@ -49,7 +49,7 @@ obj-$(CONFIG_PV) += ioport_emulate.o
 obj-y += irq.o
 obj-$(CONFIG_KEXEC) += machine_kexec.o
 obj-y += mm.o x86_64/mm.o
-obj-$(CONFIG_HVM) += monitor.o
+obj-$(CONFIG_VM_EVENT) += monitor.o
 obj-y += mpparse.o
 obj-y += nmi.o
 obj-y += numa.o