xen/pciback: Document when the 'unbind' and 'bind' functions are called.
xen/pciback: Document when the 'unbind' and 'bind' functions are called.

And also mention that you cannot do any pci_reset_function,
pci_reset_slot, or such calls. This is because they take the same
lock as SysFS does - and we would end up with a dead-lock if
we call those functions.

Signed-off-by: Konrad Rzeszutek Wilk <da3a51b335cef0eb0e2c329c5ef6bcd6acef687a@oracle.com>
Reviewed-by: David Vrabel <b9d45bd1f671e508cd8daa63dfc3cabb597562df@citrix.com>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs