soc/intel/xeon_sp: Add PCIe root port driver

soc/intel/xeon_sp: Add PCIe root port driver

The driver sets ACPI names for PCIe root ports and its subordinate
devices, and fill SSDT for them accordingly. SPR PCIe root port
devices are initially supported.

TEST=Build and boot on intel/archercity CRB

Change-Id: I81bd5d5a2e62301543a332162a5a789e0793e18e
Signed-off-by: Shuo Liu <shuo.liu@intel.com>
Signed-off-by: Jincheng Li <jincheng.li@intel.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/81567
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Lean Sheng Tan <sheng.tan@9elements.com>