mhi: pci_generic: Add support for reset

Add support for resetting the device, reset can be triggered in case
of error or manually via sysfs (/sys/bus/pci/devices/*/reset).

Signed-off-by: Loic Poulain <loic.poulain@linaro.org>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>