Add FlagM2 to HWCAP feature bits

FlagM2 (bit 39, kAXFlag to VIXL) was missing from the HWCAP feature bits used
for mapping Linux's feature reporting to VIXL. This caused subsequent bits to be
off by one.

src/aarch64/cpu-aarch64.cc

@@ -279,17 +279,18 @@ CPUFeatures CPU::InferCPUFeaturesFromOS(
        CPUFeatures::kSVEBitPerm,
        CPUFeatures::kSVESHA3,
        CPUFeatures::kSVESM4,
-       CPUFeatures::kFrintToFixedSizedInt,
+       CPUFeatures::kAXFlag,
        // Bits 40-47
+       CPUFeatures::kFrintToFixedSizedInt,
        CPUFeatures::kSVEI8MM,
        CPUFeatures::kSVEF32MM,
        CPUFeatures::kSVEF64MM,
        CPUFeatures::kSVEBF16,
        CPUFeatures::kI8MM,
        CPUFeatures::kBF16,
        CPUFeatures::kDGH,
-       CPUFeatures::kRNG,
        // Bits 48+
+       CPUFeatures::kRNG,
        CPUFeatures::kBTI};
 
   uint64_t hwcap_low32 = getauxval(AT_HWCAP);