bus: mhi: pci_generic: Implement PCI shutdown callback

Deinit the device on shutdown to halt MHI/PCI operation on device
side. This change fixes floating device state with some hosts that
do not fully shutdown PCIe device when rebooting.

Signed-off-by: Loic Poulain <loic.poulain@linaro.org>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Link: https://lore.kernel.org/r/1616169037-7969-1-git-send-email-loic.poulain@linaro.org
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>