KVM: SEV: Avoid WBINVD for HVA-based MMU notifications for SNP

With SNP/guest_memfd, private/encrypted memory should not be mappable,
and MMU notifications for HVA-mapped memory will only be relevant to
unencrypted guest memory. Therefore, the rationale behind issuing a
wbinvd_on_all_cpus() in sev_guest_memory_reclaimed() should not apply
for SNP guests and can be ignored.

Signed-off-by: Ashish Kalra <ashish.kalra@amd.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
[mdr: Add some clarifications in commit]
Signed-off-by: Michael Roth <michael.roth@amd.com>
Message-ID: <20240501085210.2213060-17-michael.roth@amd.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>