sunxi: simplify ACTLR.SMP bit set #ifdef

Instead of enumerating all SoC families that need that bit set, let's
just express this more clearly: The SMP bits needs to be set on
SMP capable ARMv7 CPUs. It's much easier in Kconfig to express it the
other way round, so we use ! CPU_IS_UP and ! ARM64.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Acked-by: Maxime Ripard <maxime.ripard@free-electrons.com>