Move aarch64_linux_prepare_to_resume to nat/aarch64-linux.c

Move aarch64_linux_prepare_to_resume to nat/aarch64-linux.c

gdb:

2015-08-25  Yao Qi  <yao.qi@linaro.org>

	* Makefile.in (aarch64-liunx.o): New rule.
	(HFILES_NO_SRCDIR): Add aarch64-linux.h.
	* config/aarch64/linux.mh (NAT_FILE): Add aarch64-linux.o.
	* aarch64-linux-nat.c: Include nat/aarch64-linux.h.
	* aarch64-linux-nat.c (aarch64_get_debug_reg_state): Make it
	extern.
	(aarch64_linux_prepare_to_resume): Move it nat/aarch64-linux.c.
	* nat/aarch64-linux-hw-point.h (aarch64_debug_reg_state): Declare
	* nat/aarch64-linux.c: New file.
	* nat/aarch64-linux.h: New file.

gdb/gdbserver:

2015-08-25  Yao Qi  <yao.qi@linaro.org>

	* Makefile.in (aarch64-linux.o): New rule.
	* configure.srv (aarch64*-*-linux*): Append aarch64-linux.o to
	srv_tgtobj.
	* linux-aarch64-low.c: Include nat/aarch64-linux.h.
	(aarch64_init_debug_reg_state): Make it extern.
	(aarch64_linux_prepare_to_resume): Remove.