rs6000: Don't use rs6000_cpu_attr directly

rs6000: Don't use rs6000_cpu_attr directly

In some places in the code we currently use rs6000_cpu_attr, although
that is a cast from rs6000_tune.  This patch changes things to be more
regular and clearer.  Now rs6000_cpu_attr is not used any more, and
it is deleted.

	* config/rs6000/rs6000.h (rs6000_cpu_attr): Delete.
	* config/rs6000/rs6000.c (rs6000_variable_issue_1): Use rs6000_tune
	instead of rs6000_cpu_attr.
	(rs6000_adjust_cost): Ditto.
	(is_microcoded_insn): Ditto.
	(rs6000_adjust_priority): Ditto.
	(rs6000_issue_rate): Ditto.
	(rs6000_use_sched_lookahead): Ditto.
	(rs6000_use_sched_lookahead_guard): Ditto.
	(rs6000_sched_reorder): Ditto.
	(force_new_group): Ditto.
	* config/rs6000/rs6000.md (cpu attribute): Ditto.
	(group_ending_nop): Ditto.

From-SVN: r255463