docs: tpm: Clarify omission or removal of active_pcr_banks node
docs: tpm: Clarify omission or removal of active_pcr_banks node

Add a sentence to the active_pcr_banks node documentation that clarifies
that when the active_pcr_banks node is removed from the XML or when it
is omitted that the set of active PCR banks is not changed anymore.

Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=2039246
Signed-off-by: Stefan Berger <5c96973112e540fb909b13997fcd087e5bfbee96@linux.ibm.com>
Reviewed-by: Jiri Denemark <62bdf77dc47919a4d59a91822129d14633cfca81@redhat.com>

libvirt/libvirt,olafhering/libvirt,zippy2/libvirt,zippy2/libvirt,zippy2/libvirt,libvirt/libvirt,crobinso/libvirt,libvirt/libvirt,libvirt/libvirt,olafhering/libvirt,olafhering/libvirt,jfehlig/libvirt,zippy2/libvirt,crobinso/libvirt,jfehlig/libvirt,olafhering/libvirt,jfehlig/libvirt,crobinso/libvirt,crobinso/libvirt,jfehlig/libvirt