KVM: x86: Don't inject PV async #PF if SEND_ALWAYS=0 and guest state is protected

KVM: x86: Don't inject PV async #PF if SEND_ALWAYS=0 and guest state is protected

Don't inject PV async #PFs into guests with protected register state, i.e.
SEV-ES and SEV-SNP guests, unless the guest has opted-in to receiving #PFs
at CPL0.  For protected guests, the actual CPL of the guest is unknown.

Note, no sane CoCo guest should enable PV async #PF, but the current state
of Linux-as-a-CoCo-guest isn't entirely sane.

Fixes: add5e2f04541 ("KVM: SVM: Add support for the SEV-ES VMSA")
Link: https://lore.kernel.org/r/20250215010609.1199982-2-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>