Rename emit_insn to aarch64_emit_insn

Rename emit_insn to aarch64_emit_insn

As emit_insn becomes extern, the prefix "aarch64_" is needed.  This
patch renames emit_insn to aarch64_emit_insn.

gdb:

2015-10-12  Yao Qi  <yao.qi@linaro.org>

	* arch/aarch64-insn.c (emit_insn): Rename to ...
	(aarch64_emit_insn): ... it.  All callers updated.

gdb/gdbserver:

2015-10-12  Yao Qi  <yao.qi@linaro.org>

	* linux-aarch64-low.c: Update all callers of function renaming
	from emit_insn to aarch64_emit_insn.