PCI: keystone: Set device ID based on SoC to support multiple ports

PCI: keystone: Set device ID based on SoC to support multiple ports

K2E SoC has two PCI ports.  The SATA controller is connected to second PCI
port (port 1).  To support multiple port handling in Keystone PCI driver,
read the PCI device ID dynamically by iomap/read/unmap during probe and
save it in driver's private data and update it in host init code.  The PCI
device ID field in the RC's config space is not filled by default by the
hardware and has to be updated by the PCI driver by reading the same from
the SoC register indicated by reg index #2 in DT bindings.

Signed-off-by: Murali Karicheri <m-karicheri2@ti.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>