powerpc64/module elfv1: Set opd addresses after module relocation

module_frob_arch_sections() is called before the module is moved to its
final location. The function descriptor section addresses we are setting
here are thus invalid. Fix this by processing opd section during
module_finalize()

Fixes: 5633e85b ("powerpc64: Add .opd based function descriptor dereference")
Cc: stable@vger.kernel.org # v4.16
Signed-off-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>