ARM: Implement fault classes.

Implement some fault classes using the curriously recurring template pattern,
similar to SPARCs.
diff --git a/src/arch/arm/isa_traits.hh b/src/arch/arm/isa_traits.hh
index 542174b..91c51c4 100644
--- a/src/arch/arm/isa_traits.hh
+++ b/src/arch/arm/isa_traits.hh
@@ -104,6 +104,8 @@
     const int WordBytes = 4;
     const int HalfwordBytes = 2;
     const int ByteBytes = 1;
+
+    const uint32_t HighVecs = 0xFFFF0000;
 };
 
 using namespace ArmISA;