powerpc: Move VSX load/stores into ppc-opcode.h

Cleans up the VSX load/store instructions by moving them into
ppc-opcode.h.

Signed-off-by: Michael Neuling <mikey@neuling.org>
Acked-by: Kumar Gala <galak@kernel.crashing.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>