Absolute and relative operands on AArch64: disallow?

opnd_is_memory_ref() should check for absolute addr not only for X86_64 but for X64 overall.

https://github.com/DynamoRIO/dynamorio/blob/4f9b46023f05c1cfb756e0c61085715a0126b657/core/arch/opnd_shared.c#L1002

opnd_create_far_abs_addr() creates relative opnd but still assigns the ABS_ADDR_kind flag to the opnd. Hence, if this function is called on aarch64, opnd_is_memory_ref() will incorrectly return false.