arm64: Fix errata workarounds that depend on smccc

Some arm64 errata depend on calling into the firmware via the SMCCC
interface. This needs to happen after the psci driver has attached
as they share the interface.

Fix this by allowing the workarounds to mark when they depend on
device drivers attaching.

This is only an issue on CPU 0 as the workarounds are applied later
for the non-boot CPUs.

Reviewed by: emaste
Sponsored by: Arm Ltd
Differential Revision: https://reviews.freebsd.org/D41916