Add SVE register defines

Add all the SVE register defines used by the later patches.

In order to prevent gaps in the register numbering, the Z registers
reuse the V register numbers (which become pseudos on SVE).

2018-05-11  Alan Hayward  <alan.hayward@arm.com>

	* aarch64-tdep.c (aarch64_sve_register_names): New const
	var.
	* arch/aarch64.h (enum aarch64_regnum): Add SVE entries.
	(AARCH64_SVE_Z_REGS_NUM): New define.
	(AARCH64_SVE_P_REGS_NUM): Likewise.
	(AARCH64_SVE_NUM_REGS): Likewise.