tpm20: fix suspend/resume and entropy harvesting

[kevans]

Summary

There were a few problem here:

• TPM2_Shutdown results in a response that we need to either process or ignore, otherwise any tpm20_write or tpm20_harvest call will trivially hang on an sc->pending_data_length != 0
• We should have a matching TPM2_Startup upon resume to restore any state that should have persisted
• We must drain the harvest task before we suspend to avoid problems there

Fixes: 3deb21f1afd5 ("random: TPM_HARVEST should have been [...]")
Co-authored-by: markj (D53835)

[kevans]

This has been lightly tested, but additional validation would be appreciated.

[garga]

I'm gonna test it on my laptop but I believe you should uncomment tpm device on GENERIC together with this change

[kevans]

In D55074#1258796, @garga wrote:

I'm gonna test it on my laptop but I believe you should uncomment tpm device on GENERIC together with this change

Thanks!

re: GENERIC, I'd prefer to evaluate that independently- these fixes are still necessary standalone, and it'd be good to have a clean version for MFC.

[emaste]

Agree with @kevans, we should get this fixed first and re-enable after some wider testing.

[garga]

It works perfectly here. I've added tpm to kernel and suspended / resumed lots of times. Thank you!