[ARC] Fix and extend features of .cpu directive.

[ARC] Fix and extend features of .cpu directive.

gas/
2016-11-18  Claudiu Zissulescu  <claziss@synopsys.com>

	* testsuite/gas/arc/cl-warn.s: New file.
	* testsuite/gas/arc/cpu-pseudop-1.d: Likewise.
	* testsuite/gas/arc/cpu-pseudop-1.s: Likewise.
	* testsuite/gas/arc/cpu-pseudop-2.d: Likewise.
	* testsuite/gas/arc/cpu-pseudop-2.s: Likewise.
	* testsuite/gas/arc/cpu-warn2.s: Likewise.
	* config/tc-arc.c (selected_cpu): Initialize.
	(feature_type): New struct.
	(feature_list): New variable.
	(arc_check_feature): New function.
	(arc_select_cpu): Check for .cpu duplicates. Don't overwrite the
	current cpu features. Check if a feature is available for a given
	cpu.
	(md_parse_option): Test if features are available for a given cpu.