aarch64 multi-arch (part 3): get thread area

aarch64 multi-arch (part 3): get thread area

With the kernle fix <http://lists.infradead.org/pipermail/linux-arm-kernel/2015-July/356511.html>,
aarch64 GDB is able to read the base of thread area of 32-bit arm
program through NT_ARM_TLS.

This patch is to teach both GDB and GDBserver to read the base of
thread area correctly in the multi-arch case.  A new function
aarch64_ps_get_thread_area is added, and is shared between GDB and
GDBserver.

With this patch applied, the following fails in multi-arch testing
(GDB is aarch64 but the test cases are arm) are fixed,

 -FAIL: gdb.threads/tls-nodebug.exp: thread local storage
 -FAIL: gdb.threads/tls-shared.exp: print thread local storage variable
 -FAIL: gdb.threads/tls-so_extern.exp: print thread local storage variable
 -FAIL: gdb.threads/tls-var.exp: print tls_var
 -FAIL: gdb.threads/tls.exp: first thread local storage
 -FAIL: gdb.threads/tls.exp: first another thread local storage
 -FAIL: gdb.threads/tls.exp: p a_thread_local
 -FAIL: gdb.threads/tls.exp: p file2_thread_local
 -FAIL: gdb.threads/tls.exp: p a_thread_local second time

gdb:

2015-09-18  Yao Qi  <yao.qi@linaro.org>

	* nat/aarch64-linux.c: Include elf/common.h,
	nat/gdb_ptrace.h, asm/ptrace.h and sys/uio.h.
	(aarch64_ps_get_thread_area): New function.
	* nat/aarch64-linux.h: Include gdb_proc_service.h.
	(aarch64_ps_get_thread_area): Declare.
	* aarch64-linux-nat.c (ps_get_thread_area): Call
	aarch64_ps_get_thread_area.

gdb/gdbserver:

2015-09-18  Yao Qi  <yao.qi@linaro.org>

	* linux-aarch64-low.c: Don't include sys/uio.h.
	(ps_get_thread_area): Call aarch64_ps_get_thread_area.