[ARC] Enable code density frame option for elf targets.

xxxx-xx-xx  Claudiu Zissulescu  <claziss@synopsys.com>

	* config/arc/arc.opt (mcode-density-frame): Get the inital value
	from TARGET_CODE_DENSITY_FRAME_DEFAULT.
	* config/arc/elf.h (TARGET_CODE_DENSITY_FRAME_DEFAULT): Define.
	* config/arc/linux.h (TARGET_CODE_DENSITY_FRAME_DEFAULT): Define.
	* config/arc/arc.md (pop_multi_fp_blink): Adjust constraints to
	match what the ops is doing.
	(push_multi_fp_blink): Likewise.
	* config/arc/arc.c (arc_override_options): Enable enter/leave when
	compiling for size and elf target.
	(arc_save_callee_enter): Adjust note to match what enter/leave
	operation does.

From-SVN: r269758