powerpc/vdso: Remove unnecessary ifdefs in vdso_pagelist initialization

No need of all those #ifdefs around the pagelist initialisation,
use IS_ENABLED(), GCC will kick out unused static variables.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/f9333432e329b1fcbbbf846cb1cd4a1c4127a60b.1601197618.git.christophe.leroy@csgroup.eu