powerpc/ptrace: Enable support for TM SPR state

This patch enables support for TM SPR state related ELF core
note NT_PPC_TM_SPR based ptrace requests through PTRACE_GETREGSET,
PTRACE_SETREGSET calls. This is achieved through adding a register
set REGSET_TM_SPR in powerpc corresponding to the ELF core note
section added. It implements the get, set and active functions for
this new register set added.

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>