powerpc/pseries: Support firmware disable of RFI flush

CVE-2018-3639 (powerpc)

Some versions of firmware will have a setting that can be configured
to disable the RFI flush, add support for it.

Fixes: 8989d568 ("powerpc/pseries: Query hypervisor for RFI flush settings")
(cherry picked from commit 582605a4)
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Juerg Haefliger <juergh@canonical.com>

arch/powerpc/platforms/pseries/setup.c

@@ -522,7 +522,8 @@ static void pseries_setup_rfi_flush(void)
 		if (types == L1D_FLUSH_NONE)
 			types = L1D_FLUSH_FALLBACK;
 
-		if (!(result.behaviour & H_CPU_BEHAV_L1D_FLUSH_PR))
+		if ((!(result.behaviour & H_CPU_BEHAV_L1D_FLUSH_PR)) ||
+		    (!(result.behaviour & H_CPU_BEHAV_FAVOUR_SECURITY)))
 			enable = false;
 	} else {
 		/* Default to fallback if case hcall is not available */