kvm: x86: mmu: Rename spte_is_locklessly_modifiable()

This change renames spte_is_locklessly_modifiable() to
spte_can_locklessly_be_made_writable() to distinguish it from other
forms of lockless modifications. The full set of lockless modifications
is covered by spte_has_volatile_bits().

Signed-off-by: Junaid Shahid <junaids@google.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>