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

[Angel Pons (Code Review)]

Attention is currently required from: Hung-Te Lin, Arthur Heymans, Shelley Chen, Furquan Shaikh, Paul Menzel, Jianjun Wang.
Angel Pons has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/56791 )

Change subject: soc/mediatek: Add PCIe support
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Patch Set 18:

(1 comment)

File src/soc/mediatek/common/include/soc/pcie_common.h:

https://review.coreboot.org/c/coreboot/+/56791/comment/3cee4f5c_29956215 
PS18, Line 20: struct mtk_pcie_mmio_res *mmio_res_io;
             : 	struct mtk_pcie_mmio_res *mmio_res_mem;
I think you can use read-only pointers (pointers to const) here:

const struct mtk_pcie_mmio_res *mmio_res_io;
 const struct mtk_pcie_mmio_res *mmio_res_mem;

These are pointers to `const struct mtk_pcie_mmio_res`. This allows constifying the structs in CB:56792 without getting compile-time errors.