runqemu: Enable virtio RNG for all platforms

We have problems where systems simply stop booting and hang. This is due
to a lack of entropy which means ssh keys and networking can't be brought
up. Adding in the virtio-rng passthrough support allows host entropy to
pass into the guess and avoids these hangs.

This is particularly problematic after the gnutls upgrade which starts
using /dev/random instead of /dev/urandom but was an issue we'd occasionally
seem before that.

It particualrly affected x86 and ppc machines for some reason.

(From OE-Core rev: 51b001909f1856c45cf87091d6e4446c266d5786)

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

scripts/runqemu

@@ -806,6 +806,9 @@ class BaseConfig(object):
 
         self.qemu_opt = "%s %s %s %s %s %s" % (qemu_bin, self.get('NETWORK_CMD'), self.qemu_opt_script, self.get('ROOTFS_OPTIONS'), self.get('QB_DTB'), self.get('QB_OPT_APPEND'))
 
+        # Enable virtio RNG else we can run out of entropy in guests
+        self.qemu_opt += " -device virtio-rng-pci"
+
         if self.serialstdio:
             logger.info("Interrupt character is '^]'")
             cmd = "stty intr ^]"