pci: switch: Add PCIe switch driver

The driver supports switches connected to the PCIe root port controller.
The driver can be used to run any erratas specific to the switch
for the corresponding bus, device and function for a specific vendor
and device ID of the switch.

Change-Id: I2e2fa1d92e0292102716e978c303d9a64e9cd861
Signed-off-by: Siddartha Mohanadoss <smohanad@codeaurora.org>