powerpc/bpf: Introduce __PPC_SH64()

powerpc/bpf: Introduce __PPC_SH64()

BugLink: http://bugs.launchpad.net/bugs/1585741
Introduce __PPC_SH64() as a 64-bit variant to encode shift field in some
of the shift and rotate instructions operating on double-words. Convert
some of the BPF instruction macros to use the same.

Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
(cherry picked from linux-next commit c233f5979b3dbb39a5b2473b5fcaf58baec8f1bd)
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>