KVM x86 misc changes for 6.15:
- Fix a bug in PIC emulation that caused KVM to emit a spurious KVM_REQ_EVENT.
- Add a helper to consolidate handling of mp_state transitions, and use it to
clear pv_unhalted whenever a vCPU is made RUNNABLE.
- Defer runtime CPUID updates until KVM emulates a CPUID instruction, to
coalesce updates when multiple pieces of vCPU state are changing, e.g. as
part of a nested transition.
- Fix a variety of nested emulation bugs, and add VMX support for synthesizing
nested VM-Exit on interception (instead of injecting #UD into L2).
- Drop "support" for PV Async #PF with proctected guests without SEND_ALWAYS,
as KVM can't get the current CPL.
- Misc cleanups