[S] Change in coreboot[master]: drivers/spi/tpm: Wait for STS_COMMAND_READY

[Yu-Ping Wu (Code Review)]

Attention is currently required from: Christian Walter, Andrey Pronin.

Yu-Ping Wu has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/71724 )

Change subject: drivers/spi/tpm: Wait for STS_COMMAND_READY
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Patch Set 1:

(1 comment)

Commit Message:

https://review.coreboot.org/c/coreboot/+/71724/comment/df690105_daabb473 
PS1, Line 8: 
Andrey, I need your opinion about the following questions:

1. Should we apply same the logic for Cr50? How about non-Google TPMs?
2. Do we need to keep calling `write_tpm_sts`? Or just need to write once and waiting for `read_tpm_sts` to return the expected status?
3. What's the suggested timeout (currently 1ms)?
4. What's the suggested delay in the loop (currently 10us)?