arm64: Support a shared release for spin-table

When releasing multiple CPUs that share a release address we need them
to wait for their turn to boot. Add a mechanism to do this by booting
them until they enable the TLB before waiting their turn to enter
init_secondary.

Reviewed by: jhibbits, kevans
Sponsored by: Arm Ltd
Differential Revision: https://reviews.freebsd.org/D45082