KVM: x86: Disallow guest CPUID lookups when IRQs are disabled

Now that KVM has a framework for caching guest CPUID feature flags, add
a "rule" that IRQs must be enabled when doing guest CPUID lookups, and
enforce the rule via a lockdep assertion.  CPUID lookups are slow, and
within KVM, IRQs are only ever disabled in hot paths, e.g. the core run
loop, fast page fault handling, etc.  I.e. querying guest CPUID with IRQs
disabled, especially in the run loop, should be avoided.

Link: https://lore.kernel.org/r/20230815203653.519297-16-seanjc@google.com


Signed-off-by: Sean Christopherson <seanjc@google.com>