aarch64: add HXT Phecda core memory operation ifuncs

Phecda is HXT semiconductor's CPU core, this patch adds memory operation
ifuncs for it: sharing the same optimized implementation with Qualcomm's
Falkor core.

2018-06-07  Minfeng Kang <minfeng.kang@hxt-semitech.com>
	    Hongbo Zhang <hongbo.zhang@linaro.org>

	* sysdeps/aarch64/multiarch/memcpy.c (libc_ifunc): reuse
	__memcpy_falkor for phecda core.
	* sysdeps/aarch64/multiarch/memmove.c (libc_ifunc): reuse
	__memmove_falkor for phecda core.
	* sysdeps/aarch64/multiarch/memset.c (libc_ifunc): reuse
	__memset_falkor for phecda core.
	* sysdeps/unix/sysv/linux/aarch64/cpu-features.c: add MIDR entry
	for phecda core.
	* sysdeps/unix/sysv/linux/aarch64/cpu-features.h (IS_PHECDA): add
	macro to identify phecda core.