[RS6000] power8 unaligned fp load/store

[RS6000] power8 unaligned fp load/store

According to the POWER8 Processor User’s Manual and some
experimentation on power8 hardware, unaligned fp load/store on power8
does not invoke the alignment interrupt.

	* config/rs6000/rs6000.h (SLOW_UNALIGNED_ACCESS): Make scalar
	float access depend on TARGET_EFFICIENT_UNALIGNED_VSX.
	* config/rs6000/rs6000.opt (-mefficient-unaligned-vsx): Renamed
	from -mefficient-unaligned-vector.  Note that this affects fp too.

git-svn-id: svn+ssh://gcc.gnu.org/svn/gcc/trunk@239013 138bc75d-0d04-0410-961f-82ee72b054a4