The arm PJ4B cpu is armv7 architecture, not v6.

If this feels like deja vu... the last time this was fixed in this file
only ARM_MMU_V6 was fixed, this time it's ARM_ARCH_V6 (and this time I
searched for other occurrances of pj4b in here).


git-svn-id: svn+ssh://svn.freebsd.org/base/head@274941 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f