rs6000: Split rs6000_cpu

rs6000: Split rs6000_cpu

This splits rs6000_cpu into rs6000_cpu and rs6000_tune.  Both are still
initialised identically, so there is no behaviour change.

Now rs6000_cpu should be set by -mcpu=, and rs6000_tune by -mtune= (but
both still are set by -mtune=, fixed in a later patch in the series).

Also change rs6000_cpu to rs6000_tune in the appropriate cases (i.e.
most, but not those that enable using new insns).

	* config/rs6000/rs6000.opt (rs6000_tune): New variable.
	* config/rs6000/rs6000.c (rs6000_option_override_internal): Also set
	rs6000_tune.  Use rs6000_tune instead of rs6000_cpu where appropriate.
	(rs6000_loop_align): Use rs6000_tune instead of rs6000_cpu where
	appropriate.
	(rs6000_reassociation_width): Ditto.
	(rs6000_emit_epilogue): Ditto.
	(rs6000_adjust_cost): Ditto.
	(is_microcoded_insn): Ditto.
	(is_cracked_insn): Ditto.
	(rs6000_adjust_priority): Ditto.
	(rs6000_sched_reorder): Ditto.
	(rs6000_sched_reorder2): Ditto.
	(insn_must_be_first_in_group): Ditto.
	(insn_must_be_last_in_group): Ditto.
	(rs6000_register_move_cost): Ditto.
	* config/rs6000/rs6000.h (rs6000_cpu_attr): Use rs6000_tune instead of
	rs6000_cpu.

From-SVN: r255462