amd64/vmm: Don't advertise support for performance counters

vmm doesn't implement them, and after commit 2272fac218
("hwpmc: Add support for AMD-only IRPERF in hwpmc PERF class"), FreeBSD
guests fail to boot since they access the unimplemented IRPERF MSR.

MFC after:	1 week

sys/amd64/vmm/x86.c

@@ -137,8 +137,7 @@ x86_emulate_cpuid(struct vcpu *vcpu, uint64_t *rax, uint64_t *rbx,
 				 * unsupported or unsafe AMD extended features
 				 * (8000_0008 EBX).
 				 */
-				regs[1] &= (AMDFEID_CLZERO | AMDFEID_IRPERF |
-				    AMDFEID_XSAVEERPTR);
+				regs[1] &= AMDFEID_CLZERO | AMDFEID_XSAVEERPTR;
 
 				vm_get_topology(vm, &sockets, &cores, &threads,
 				    &maxcpus);