Refactor arm_stack_frame_destroyed_p

Refactor arm_stack_frame_destroyed_p

This patch is to refactor arm_stack_frame_destroyed_p, so that the code
can be used in both arm_stack_frame_destroyed_p and arm epilogue
unwinder I am going to add in the next patch.  In fact, the code
is the same in two places, but checking whether it is thumb mode
is slightly different.  arm_stack_frame_destroyed_p uses
arm_pc_is_thumb, and epilogue unwinder should use arm_frame_is_thumb.

gdb:

2016-03-30  Yao Qi  <yao.qi@linaro.org>

	* arm-tdep.c (arm_stack_frame_destroyed_p): Rename it ...
	(arm_stack_frame_destroyed_p_1): ... here.  Don't call
	arm_pc_is_thumb.
	(arm_stack_frame_destroyed_p): Call
	thumb_stack_frame_destroyed_p and
	arm_stack_frame_destroyed_p_1.