aarch64: Add occmo flag for FEAT_OCCMO

FEAT_OCCMO support was introduced, but the feature flags were missing.
This patch adds these flags, as well as splitting up the tests to test
occmo vs occmo+memtag operands.

include/opcode/aarch64.h

@@ -137,6 +137,8 @@ enum aarch64_feature_bit {
   AARCH64_FEATURE_SSBS,
   /* Memory Tagging Extension.  */
   AARCH64_FEATURE_MEMTAG,
+  /* Outer Cacheable Cache Maintenance Operation.  */
+  AARCH64_FEATURE_OCCMO,
   /* Transactional Memory Extension.  */
   AARCH64_FEATURE_TME,
   /* XS memory attribute.  */