rs6000: Sanitize vector modes

rs6000: Sanitize vector modes

This removes the vector modes that were only used by SPE.  It also
rearranges things so it is easier to see what is there, and for what.

	* config/rs6000/rs6000-modes.def: Remove all 8-byte vector modes
	except V2SF and V2SI.  Rearrange the vector modes, and add comments.
	* config/rs6000/rs6000.c (rs6000_debug_reg_global): Remove V8QImode
	and V4HImode.
	(reg_offset_addressing_ok_p): Remove V4HImode and V1DImode.
	(rs6000_legitimate_offset_address_p): Ditto.
	(rs6000_emit_move): Ditto.
	(rs6000_init_builtins): Remove V4HI_type_node.

From-SVN: r249162