arm64: Consolidate hotplug notifier for instruction emulation
As of now each insn_emulation has a cpu hotplug notifier that
enables/disables the CPU feature bit for the functionality. This
patch re-arranges the code, such that there is only one notifier
that runs through the list of registered emulation hooks and runs
their corresponding set_hw_mode.
We do nothing when a CPU is dying as we will set the appropriate bits
as it comes back online based on the state of the hooks.