powerpc/dt_cpu_ftrs: Advertise support for ISA v3.1 if selected

On powernv hardware support for ISAv3.1 is advertised via a cpu feature
bit in the device tree. This patch enables the associated HWCAP bit if
the device tree indicates ISAv3.1 is available.
Signed-off-by: Alistair Popple <alistair@popple.id.au>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200521014341.29095-4-alistair@popple.id.au

arch/powerpc/kernel/dt_cpu_ftrs.c

@@ -26,6 +26,7 @@
 /* Device-tree visible constants follow */
 #define ISA_V2_07B      2070
 #define ISA_V3_0B       3000
+#define ISA_V3_1        3100
 
 #define USABLE_PR               (1U << 0)
 #define USABLE_OS               (1U << 1)
@@ -662,6 +663,11 @@ static void __init cpufeatures_setup_start(u32 isa)
 		cur_cpu_spec->cpu_features |= CPU_FTR_ARCH_300;
 		cur_cpu_spec->cpu_user_features2 |= PPC_FEATURE2_ARCH_3_00;
 	}
+
+	if (isa >= 3100) {
+		cur_cpu_spec->cpu_features |= CPU_FTR_ARCH_31;
+		cur_cpu_spec->cpu_user_features2 |= PPC_FEATURE2_ARCH_3_1;
+	}
 }
 
 static bool __init cpufeatures_process_feature(struct dt_cpu_feature *f)