Don't scan prologue past epilogue

Don't scan prologue past epilogue

This patch is to stop prologue analysis past epilogue in for arm mode,
while we've already had done the same to thumb mode (see
thumb_instruction_restores_sp).  This is useful to parse functions
with empty body (epilogue follows prologue).

gdb:

2014-12-12  Yao Qi  <yao@codesourcery.com>

	* arm-tdep.c (arm_instruction_restores_sp): New function.
	(arm_analyze_prologue): Call arm_instruction_restores_sp.
	(arm_in_function_epilogue_p): Move code to
	arm_instruction_restores_sp.