Add FEAT_LRCPC support to the aarch64 decoder
Our armv8.2 processors have FEAT_LRCPC (lrcpc in Linux cpuinfo) and our binaries are executing opcodes like LDAPR yet DR's decoder does not decode it, causing drmemtrace to not trace it, and possibly leading to crashes when it is inside rseq regions (that is still being investigated; we are not 100% sure that is the cause; will be filed separately):
$ disasm_a64 f8bfc0c5
bfd: f8bfc0c5 ldapr x5, [x6]
DynamoRIO: f8bfc0c5 xx $0xf8bfc0c5 %x5 %x6 %x16 %sp -> %x5 %x6 %x16 %sp