PCI: spear: Add PCIe driver for ST Microelectronics SPEAr13xx
ARM based ST Microelectronics's SPEAr1310 and SPEAr1340 SOCs have onchip
designware PCIe controller. To make that usable, this patch adds a wrapper
driver based on existing designware driver.
Adds bindings for this new driver and update MAINTAINERS as well.