Tidy up glitches in XML feature descriptions. Work in progress.

	* features/arc-aux-baseline.v1.xml: replace dccm_build by isa_config.
	* features/arc-core-other.xml: Correct feature name.
Complete analysis of target description. Work in progress.

	* arc-tdep.c (arc_sim_aux_map_size): Initialize in
	arc_gdbarch_init each time.
	(arc_register_name, arc_register_type): Temporarily reinstated.
	(arc_gdbarch_init): record first and last saved reg names in
	arc_regnum. Record current feature name in variables. Initialize
	arc_sim_aux_map_size each time. Correct sets of temp and saved
	registers. Provide warnings for all tdesc failures.
	* arc-tdep.h (ARC_REDUCED_FIRST_SAVED_REGNUM)
	(ARC_REDUCED_LAST_SAVED_REGNUM, ARC_FIRST_EXTENSION_REGNUM)
	(ARC_LAST_EXTENSION_REGNUM): New #define values.
	(struct arc_regnum): Add first_saved_regnum and last_saved_regnum
	fields.