Log Message:
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arm: Remove HVC dispatching to PSCI services
The root cell can't be using HVC dispatching as it can't be running a
hypervisor prior to Jailhouse. And we can tell our non-root cells to use
the SMC method for PSCI services.
Reject every SMC requests except for the emulated PSCI services. This is
required because we have generally no idea about what services are
behind an interface, and even the calling convention is undefined.
Better fail loudly and then resolve the valid cases on a per-platform
basis.
This obsoletes the smc stub in exception.S, so remove it.