KVM: PPC: Book3S HV: Disallow LPCR[AIL] to be set to 1 or 2

These are already disallowed by H_SET_MODE from the guest, also disallow
these by updating LPCR directly.

AIL modes can affect the host interrupt behaviour while the guest LPCR
value is set, so filter it here too.

Suggested-by: Fabiano Rosas <farosas@linux.ibm.com>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Acked-by: Paul Mackerras <paulus@ozlabs.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210412014845.1517916-5-npiggin@gmail.com