rs6000.md/altivec.md problem in setting of vector registers

[David Edelsohn]

> There are several cost-computation functions in rs6000.c, especially
> rs6000_register_move_cost looks promising.  Doesn't the RA call into there
> at some point?  Seems like it should.  That would be the right place, if
> it does.

	REGISTER_MOVE_COST only is provided the mode and register classes,
not the actual instruction, so it has no knowledge about the operands.
The costs is not wrong, but the RA is inquiring about the wrong mode.
Either RA needs to ask about the correct mode or insv needs to generate
patterns for vector types.

David