sysutils/py-py-cpuinfo: fix on armv7, add lscpu dependency

On FreeBSD, armv[67] both report "arm" in "uname -m", but this package
expected the string armv6 or armv7. Fix the port by adding an extra
case for just "arm" to the architecture detection logic.

While we are at it, optionally depend on sysutils/lscpu as an
additional data source for architecture features.

See also: https://github.com/workhorsy/py-cpuinfo/issues/197
Approved by: yuri (maintainer)
Differential Revision: https://reviews.freebsd.org/D40252