bus: mhi: pci-generic: Fix hibernation

This patch fixes crash after resuming from hibernation. The issue
occurs when mhi stack is builtin and so part of the 'restore-kernel',
causing the device to be resumed from 'restored kernel' with a no
more valid context (memory mappings etc...) and leading to spurious
crashes.

This patch fixes the issue by implementing proper freeze/restore
callbacks.

Link: https://lore.kernel.org/r/1622571445-4505-1-git-send-email-loic.poulain@linaro.org
Reported-by: Shujun Wang <wsj20369@163.com>
Cc: stable <stable@vger.kernel.org>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Signed-off-by: Loic Poulain <loic.poulain@linaro.org>
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Link: https://lore.kernel.org/r/20210606153741.20725-4-manivannan.sadhasivam@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>