Enable load of tpm driver with devd rule

[nangirl]

The devd rule comes from @tstruk proposal. The old rule was not working. This rule won't trigger if tpm driver was already loaded at boot.

[tstruk]

Looks good to me. Thanks!

[bsdimp]

This will work, though devfs is usually used instead of devd to set ownership and permissions

[LuKePicci]

@bsdimp devfs doesn't fit well to the "packaged" rule addition approach. AFAIK there's no way to include additional devfs rules by adding a file. The only devfs way would be to define such rule into something which is not part of this package. Does the _tss group exist before installing this port? Would it be fine to have devfs setting permissions to a non-existing group id?

BTW, I made a quick test on pfSense with devfs.rules by setting a new system default ruleset and extending the previous default ruleset with a new extra rule for tpm. It didn't work until I restarted devfs despite tpm.ko was correctly loaded during boot with tpm_load="YES". Not sure if pfSense is doing strange things with devfs or this tpm driver couldn't work with devfs.