Implement SystemTap SDT probe support for AArch64

This commit implements the needed bits for SystemTap SDT probe support
on AArch64 architectures.

First, I started by looking at AArch64 assembly specification and
filling the necessary options on gdbarch's stap machinery in order to
make the generic asm parser (implemented in stap-probe.c) recognize
AArch64's asm.

After my last patch for the SystemTap SDT API, which extends it in order
to accept multiple prefixes and suffixes, this patch became simpler.  I
also followed Marcus suggestion and did not shared code between 32- and
64-bit ARM.

Tom asked me in a previous message how I did my tests.  I believe I
replied that, but just in case: I ran the tests on
gdb.base/stap-probe.exp by hand.  I also managed to run the tests on
real hardware, and they pass without regressions.

2013-12-28  Sergio Durigan Junior  <sergiodj@redhat.com>

	PR tdep/15653
	* NEWS: Mention SystemTap SDT probe support for AArch64 GNU/Linux.
	* aarch64-linux-tdep.c: Include necessary headers for parsing of
	SystemTap SDT probes.
	(aarch64_stap_is_single_operand): New function.
	(aarch64_stap_parse_special_token): Likewise.
	(aarch64_linux_init_abi): Declare SystemTap SDT probe argument
	prefixes and suffixes.  Initialize gdbarch with them.