Push down Giant one layer. In the days of yore, back when Penitums
were the new kids on the block and F00F hacks were all the rage, one
needed to take out Giant to do anything moderately complicated with
the VM, mappings and such. So the pccard / cardbus code held Giant for
the entire insertion or removal process.

Today, the VM is MP safe. The lock is only needed for dealing with
newbus things. Move locking and unlocking Giant to be only around
adding and probing devices in pccard and cardbus.