PCI: dwc: Add API support to de-initialize host

Add an API to group all the tasks to be done to de-initialize host which
can then be called by any dwc core based driver implementations
while adding .remove() support in their respective drivers.

Signed-off-by: Vidya Sagar <vidyas@nvidia.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Acked-by: Gustavo Pimentel <gustavo.pimentel@synopsys.com>