x86: allow disabling all emulated devices inside of Xen

Only allow enabling or disabling all the emulated devices inside of Xen,
right now Xen doesn't support enabling specific emulated devices only.

Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>

xen/arch/x86/domain.c

@@ -532,8 +532,8 @@ int arch_domain_create(struct domain *d, unsigned int domcr_flags,
                    d->domain_id, config->emulation_flags);
             return -EINVAL;
         }
-        if ( is_hvm_domain(d) ? (config->emulation_flags != XEN_X86_EMU_ALL)
-                              : (config->emulation_flags != 0) )
+        if ( config->emulation_flags != 0 &&
+             (!is_hvm_domain(d) || config->emulation_flags != XEN_X86_EMU_ALL) )
         {
             printk(XENLOG_G_ERR "d%d: Xen does not allow %s domain creation "
                    "with the current selection of emulators: %#x\n",