ossl(4): Install the man page also for arm64

In 22bd0c9731d7 ossl(4) was ported to arm64. The manual page was
adapted, but never installed since the ossl(4) manual page was
i386 / amd64 only.

Reviewed by: mhorne
Differential Revision: https://reviews.freebsd.org/D29762

(cherry picked from commit b1ab802ce4908b6af93e3a3b4328377003735357)