Convert KVM specific system vectors to IDTENTRY_SYSVEC*:

The two empty stub handlers which only increment the stats counter do no
need to run on the interrupt stack. Use IDTENTRY_SYSVEC_SIMPLE for them.

The wakeup handler does more work and runs on the interrupt stack.

None of these handlers need to save and restore the irq_regs pointer.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Acked-by: Andy Lutomirski <luto@kernel.org>
Link: https://lore.kernel.org/r/20200521202119.555715519@linutronix.de