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.

Approved by: re (gjb)
Reviewed by: emaste
Sponsored by: Arm Ltd
Differential Revision: https://reviews.freebsd.org/D41916

(cherry picked from commit c643e82dba0b17b2716de4c9d44a3c9c547cbbd5)
(cherry picked from commit 843bea18711d726cd2f0a3c3f9144b218e4de3e8)
(cherry picked from commit caf7bc535622ee7baeffc3366db8bf0e896aa018)