Change in coreboot[master]: soc/mediatek: Add PCIe support

[Jianjun Wang (Code Review)]

Attention is currently required from: Shelley Chen, Hung-Te Lin, Furquan Shaikh, Yu-Ping Wu, Jianjun Wang.
Hello Shelley Chen, Hung-Te Lin, build bot (Jenkins), Yu-Ping Wu,

I'd like you to reexamine a change. Please visit

https://review.coreboot.org/c/coreboot/+/56791

to look at the new patch set (#5).

Change subject: soc/mediatek: Add PCIe support
......................................................................

soc/mediatek: Add PCIe support

Add PCIe support for MediaTek platform.

Reference:
  - MT8195 Register Map V0.3-2, Chapter 3.18 PCIe controller (Page 1250)
  - linux/drivers/pci/controller/pcie-mediatek-gen3.c

This code is based on MT8195 platform, but it should be common in each
platform with the same PCIe IP in the future.

TEST=Build pass and boot up to kernel successfully via SSD
BUG=b:178565024

Signed-off-by: Jianjun Wang 
Change-Id: Ib9b6adaafa20aeee136372ec9564273f86776da0
---
A src/soc/mediatek/common/include/soc/pcie_common.h
A src/soc/mediatek/common/pcie.c
2 files changed, 335 insertions(+), 0 deletions(-)

git pull ssh://review.coreboot.org:29418/coreboot refs/changes/91/56791/5