arch: armv4 isn't supported either on aarch64 running in aarch32 mode

FreeBSD used to support both armv4 and armv5 binaries. All of that
support has been removed from the tree. We have only ever supported
armv6 and armv7 binaries in that mode. Note armv4 here too for
completeness since it flowed better than 'armv5 and earlier' and means
the same thing (FreeBSD never ran on an armv3 or earlier CPU).

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