ARM: fix ifdef in ARMv8 lowlevel_init() again

Commit 11661193 ("ARM: fix ifdefs in ARMv8 lowlevel_init()")
accidentally inverted the logic of CONFIG_ARMV8_MULTIENTRY.

Fixes: 11661193 ("ARM: fix ifdefs in ARMv8 lowlevel_init()")
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: Stephen Warren <swarren@nvidia.com>