[binutils][aarch64] New sve_size_sd2 iclass.

[binutils][aarch64] New sve_size_sd2 iclass.

Define new sve_size_sd2 iclass to distinguish between the two variants
of ldnt1sb and ldnt1sh.

include/ChangeLog:

2019-05-09  Matthew Malcomson  <matthew.malcomson@arm.com>

	* opcode/aarch64.h (enum aarch64_insn_class): Add sve_size_sd2 iclass.

opcodes/ChangeLog:

2019-05-09  Matthew Malcomson  <matthew.malcomson@arm.com>

	* aarch64-asm.c (aarch64_encode_variant_using_iclass): Handle
	sve_size_sd2 iclass encode.
	* aarch64-dis.c (aarch64_decode_variant_using_iclass): Handle
	sve_size_sd2 iclass decode.
	* aarch64-opc.c (fields): Handle SVE_sz2 field.
	* aarch64-opc.h (enum aarch64_field_kind): New SVE_sz2 field.