[AArch64][SVE 15/32] Add {insert,extract}_all_fields helpers

[AArch64][SVE 15/32] Add {insert,extract}_all_fields helpers

Several of the SVE operands use the aarch64_operand fields array
to store the fields that make up the operand, rather than hard-coding
the names in the C code.  This patch adds helpers for inserting and
extracting those fields.

opcodes/
	* aarch64-asm.c: Include libiberty.h.
	(insert_fields): New function.
	(aarch64_ins_imm): Use it.
	* aarch64-dis.c (extract_fields): New function.
	(aarch64_ext_imm): Use it.

Change-Id: I23658f0ea290c9a14380946c42e2d1d40997fd07