[ARC] Don't check extAuxRegister second argument for sign.

[ARC] Don't check extAuxRegister second argument for sign.

gas/
2016-12-05  Claudiu Zissulescu  <claziss@synopsys.com>

	* testsuite/gas/arc/textauxregister-1.d: New file.
	* testsuite/gas/arc/textauxregister-1.s: Likewise.
	* testsuite/gas/arc/textcondcode-err.s: Likewise.
	* testsuite/gas/arc/textcoreregister-err.s: Likewise.
	* config/tc-arc.c (tokenize_extregister): Return bfd_boolean,
	don't check second argument of extension auxiliary register for
	signess.
	(arc_extcorereg): Consider the return of tokenize_extregister
	function call.