powerpc/module_64: Convert #ifdef to IS_ENABLED()

Minor refactor for converting #ifdef to IS_ENABLED().

Reviewed-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Naveen N Rao <naveen@kernel.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://patch.msgid.link/20241030070850.1361304-6-hbathini@linux.ibm.com