KVM: nVMX: Free only guest_mode (L2) roots on INVVPID w/o EPT

When emulating INVVPID for L1, free only L2+ roots, using the guest_mode
tag in the MMU role to identify L2+ roots.  From L1's perspective, its
own TLB entries use VPID=0, and INVVPID is not requied to invalidate such
entries.  Per Intel's SDM, INVVPID _may_ invalidate entries with VPID=0,
but it is not required to do so.

Cc: Lai Jiangshan <laijs@linux.alibaba.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210609234235.1244004-10-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>