xen/spec-ctrl: Speculative mitigation facilities report wrong status

Booting with spec-ctrl=0 results in Xen printing "None MD_CLEAR".

  (XEN)   Support for HVM VMs: None MD_CLEAR
  (XEN)   Support for PV VMs: None MD_CLEAR

Add a check about X86_FEATURE_MD_CLEAR to avoid to print "None".

Signed-off-by: James Wang <jnwang@suse.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
master commit: 2adc580bd5
master date: 2019-07-31 14:53:13 +0100

xen/arch/x86/spec_ctrl.c

@@ -360,6 +360,7 @@ static void __init print_details(enum ind_thunk thunk, uint64_t caps)
     printk("  Support for HVM VMs:%s%s%s%s%s\n",
            (boot_cpu_has(X86_FEATURE_SC_MSR_HVM) ||
             boot_cpu_has(X86_FEATURE_SC_RSB_HVM) ||
+            boot_cpu_has(X86_FEATURE_MD_CLEAR)   ||
             opt_eager_fpu)                           ? ""               : " None",
            boot_cpu_has(X86_FEATURE_SC_MSR_HVM)      ? " MSR_SPEC_CTRL" : "",
            boot_cpu_has(X86_FEATURE_SC_RSB_HVM)      ? " RSB"           : "",
@@ -371,6 +372,7 @@ static void __init print_details(enum ind_thunk thunk, uint64_t caps)
     printk("  Support for PV VMs:%s%s%s%s%s\n",
            (boot_cpu_has(X86_FEATURE_SC_MSR_PV) ||
             boot_cpu_has(X86_FEATURE_SC_RSB_PV) ||
+            boot_cpu_has(X86_FEATURE_MD_CLEAR)  ||
             opt_eager_fpu)                           ? ""               : " None",
            boot_cpu_has(X86_FEATURE_SC_MSR_PV)       ? " MSR_SPEC_CTRL" : "",
            boot_cpu_has(X86_FEATURE_SC_RSB_PV)       ? " RSB"           : "",