powerpc/configs: Properly enable PAPR_SCM in pseries_defconfig

My commit to add PAPR_SCM to pseries_defconfig failed to add the
required dependencies, meaning the driver doesn't get built.

Add the required LIBNVDIMM=m.

Fixes: d6481a71 ("powerpc/configs: Add PAPR_SCM to pseries_defconfig")
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220901014253.252927-1-mpe@ellerman.id.au