for later Cortex-A CPUs that support the Multiprocessor Extensions. This
will be needed to support both in a single GENERIC kernel while still
being able to only build for a single SoC.
Reviewed by: mmel
Relnotes: yes
Sponsored by: ABT Systems Ltd
Differential Revision: https://reviews.freebsd.org/D8138
Only L2 PIPT cache is supported for __ARM_ARCH >= 6.
In fact, this is just a pure proclamation as this option is used
only in armv4 specific files now.