tpm20: fix suspend/resume and entropy harvesting

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

This commit is sufficient to avoid breaking suspend/resume.

Co-authored-by: markj
Tested by: garga

(cherry picked from commit 38a4995eb52db21116f8b37ed942e66a8c2f050f)