Add ARM Cortex A72 to CPU list

This change is required to properly detect CPUs
on Marvell Armada 80x0/70x0 SoC family.

Submitted by: Rafal Kozik <rk@semihalf.com>
Reviewed by: andrew, cognet (mentor)
Approved by: cognet (mentor)
Sponsored by: Semihalf
Differential Revision: https://reviews.freebsd.org/D12184