qemu_cpu.cfg: host_cpu_vendor variants

This will allow us to filter/document cases that require a specific host
CPU vendor. Enable only host_cpu_vendor=unknown by default.
Signed-off-by: NEduardo Habkost <ehabkost@redhat.com>

qemu/tests/cfg/qemu_cpu.cfg

@@ -33,11 +33,21 @@
                 - 1_4:
                 - 1_5:
 
+    variants host_cpu_vendor:
+        - @unknown:
+        - amd:
+        - intel:
+
     # uncomment the line corresponding to the QEMU version, if you know it:
     only (qemu_flavor = unknown)
     #only (qemu_flavor = rhel)..(rhel_version = 6_4)
     #only (qemu_flavor = upstream)..(qemu_version = 1_5)
 
+    # uncomment the line corresponding to the host CPU vendor, if you know it:
+    only (host_cpu_vendor = unknown)
+    #only (host_cpu_vendor = amd)
+    #only (host_cpu_vendor = intel)
+
     # CPU model lists:
     variants:
         - cpu.unset: