ARM: v6k: use CPU domain feature if we include support for arch < ARMv6K

Rather than turning off CPU domain switching when the build architecture
includes ARMv6K, thereby causing problems for ARMv6-supporting kernels,
turn it on when it's required to support a CPU architecture.

Acked-by: Nicolas Pitre <nicolas.pitre@linaro.org>
Acked-by: Tony Lindgren <tony@atomide.com>
Tested-by: Sourav Poddar <sourav.poddar@ti.com>
Tested-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>