powerpc: Add FP/VSX and VMX register load functions for transactional memory

This adds functions to restore the state of the FP/VSX registers from
what's stored in the thread_struct.  Two version for FP/VSX are required
since one restores them from transactional/checkpoint side of the
thread_struct and the other from the speculated side.

Similar functions are added for VMX registers.

Signed-off-by: Matt Evans <matt@ozlabs.org>
Signed-off-by: Michael Neuling <mikey@neuling.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>