Change in coreboot[master]: soc/mediatek: Add timestamp to measure PERST# time

[Yu-Ping Wu (Code Review)]

Attention is currently required from: Hung-Te Lin, Angel Pons, Jianjun Wang.
Yu-Ping Wu has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/62933 )

Change subject: soc/mediatek: Add timestamp to measure PERST# time
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Patch Set 1:

(2 comments)

File src/mainboard/google/cherry/bootblock.c:

https://review.coreboot.org/c/coreboot/+/62933/comment/dae39320_fad1d982 
PS1, Line 56: write64
We should also add read/write API for this in pcie_common.h. For example,

void mtk_pcie_save_timestamp(uint64_t timestamp);
 uint64_t mtk_pcie_load_timestamp(void);

File src/soc/mediatek/common/pcie.c:

https://review.coreboot.org/c/coreboot/+/62933/comment/1d06eeef_0b9b9b5f 
PS1, Line 238: COLLECT_TIMESTAMPS
Since the 100ms delay is a requirement, should we always do this?