[lldb][AArch64] Add test predicate for systems with SME enabled

[DavidSpickett]

Summary

"sme" is just one of many cpuinfo features for SME but it's the
only one we need for testing.

The rest are related to the use of certain instructions and
don't change the register state available.

lldb/packages/Python/lldbsuite/test/lldbtest.py

class Base(unittest2.TestCase):
     def isAArch64(self):
         """Returns true if the architecture is AArch64."""
         arch = self.getArchitecture().lower()
         return arch in ["aarch64", "arm64", "arm64e"]
 
     def isAArch64SVE(self):
         return self.isAArch64() and "sve" in self.getCPUInfo()
 
+    def isAArch64SME(self):
+        return self.isAArch64() and "sme" in self.getCPUInfo()
+
     def isAArch64MTE(self):
         return self.isAArch64() and "mte" in self.getCPUInfo()
 
     def isAArch64PAuth(self):
         if self.getArchitecture() == "arm64e":
             return True
         return self.isAArch64() and "paca" in self.getCPUInfo()