powerpc/ptrace: Enable in transaction NT_PPC_VSX ptrace requests

This patch enables in transaction NT_PPC_VSX ptrace requests. The
function vsr_get which gets the running value of all VSX registers
and the function vsr_set which sets the running value of of all VSX
registers work on the running set of VMX registers whose location
will be different if transaction is active. This patch makes these
functions adapt to situations when the transaction is active.

Signed-off-by: Anshuman Khandual <khandual@linux.vnet.ibm.com>
Signed-off-by: Simon Guo <wei.guo.simon@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>