To allow for the state of some errata to be detected we need devices,
e.g. to call into the SMCCC firmware. Because of this we need to check
this after devices drivers are ready.

As the presence of this errata may require us to mask out some fields
from the ID register views, and these register views are used to build
the userspace hwcap values and used in late kernel ifunc resolvers we
need to ensure they have run by a known point.

Add a synchronisation point for APs at SI_SUB_CONFIGURE,
SI_ORDER_MIDDLE + 1. This is early enough that we can move setting the
hwcap values just after this, and late enough for devices to be present.

Sponsored by: Arm Ltd