PCI: Give pcim_set_mwi() its own devres cleanup callback

Managing pci_set_mwi() with devres can easily be done with its own
callback, without the necessity to store any state about it in a
device-related struct.

Remove the MWI state from struct pci_devres.  Give pcim_set_mwi() a
separate devres cleanup callback.

Link: https://lore.kernel.org/r/20240613115032.29098-10-pstanner@redhat.com


Signed-off-by: Philipp Stanner <pstanner@redhat.com>
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>