powerpc/64/build: only include .opd with ELFv1

ELFv2 does not use function descriptors so .opd is not required.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220916040755.2398112-6-npiggin@gmail.com