[binutils][aarch64] New sve_size_013 iclass.

[binutils][aarch64] New sve_size_013 iclass.

Add sve_size_013 instruction class

This new iclass handles instructions such as pmullb whose size specifier
can only be encoded as 0, 1, or 3.

include/ChangeLog:

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

	* opcode/aarch64.h (enum aarch64_insn_class): Add sve_size_013 iclass.

opcodes/ChangeLog:

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

	* aarch64-asm.c (aarch64_encode_variant_using_iclass): Handle
	sve_size_013 iclass encode.
	* aarch64-dis.c (aarch64_decode_variant_using_iclass): Handle
	sve_size_013 iclass decode.