Add AArch64 hwcap values from Linux 4.17.

Linux 4.17 adds four new AArch64 hwcap values.  This patch adds them
to glibc's AArch64 bits/hwcap.h, with corresponding dl-procinfo.c
updates.

Tested with build-many-glibcs.py for aarch64.

	* sysdeps/unix/sysv/linux/aarch64/bits/hwcap.h (HWCAP_DIT): New
	macro.
	(HWCAP_USCAT): Likewise.
	(HWCAP_ILRCPC): Likewise.
	(HWCAP_FLAGM): Likewise.
	* sysdeps/unix/sysv/linux/aarch64/dl-procinfo.c (_DL_HWCAP_COUNT):
	Increase to 28.
	(_dl_aarch64_cap_flags): Add new flag names.