Rewrite to support ARC v2 ABI without regsets, which are not present in
Linux 3.2.

2013-03-05  Jeremy Bennett <jeremy.bennett@embecosm.com>

	* configure.srv (arc*-*-linux*): Add srv_usrregs for legacy.
	* linux-arc-low.c: Reorder functions for clarity and tidy up
	commenting generally.
	(struct user_regs_scratch): based on ptrace.h structs.
	(arc_arch_setup): Initalize register map for ARC v2 ABI.
	(arc_num_regs): Deleted and relaced by the_low_target.num_regs
	throughout.
	(arc_fetch_register, arc_breakpoint_at): New functions.
	(target_regsets): Correct field names.
	(the_low_target): Add entry for breakpoint_at and optionally
	fetch_register.