Determine the kind of single step breakpoint

This patch adds a new gdbarch method breakpoint_kind_from_current_state
for single step breakpoint, and uses it in breakpoint_kind.

gdb:

2016-11-03  Yao Qi  <yao.qi@linaro.org>

	* arch-utils.c (default_breakpoint_kind_from_current_state):
	New function.
	* arch-utils.h (default_breakpoint_kind_from_current_state):
	Declare.
	* arm-tdep.c (arm_breakpoint_kind_from_current_state): New
	function.
	(arm_gdbarch_init): Call
	set_gdbarch_breakpoint_kind_from_current_state.
	* breakpoint.c (breakpoint_kind): Call
	gdbarch_breakpoint_kind_from_current_state for single step
	breakpoint.  Update comments.
	* gdbarch.sh (breakpoint_kind_from_current_state): New.
	* gdbarch.c, gdbarch.h: Regenerate.