Various x2APIC fixes and enhancements:
- Use spinlocks for the vioapic.
- Handle the SELF_IPI MSR.
- Simplify the APIC mode switching between MMIO and x2APIC. The guest is
no longer allowed to switch modes at runtime. Instead, the desired mode
is set when the virtual machine is created.
- Disallow MMIO access in x2APIC mode and MSR access in xAPIC mode.
- Add support for x2APIC virtualization assist in Intel VT-x.
f6a797dc57