Feature Request : add a option to clear the tpm if exitss

[huckley]

many laptops use encryption with tpm(2).
So I guess it is a good idea to clear to add a option to clear the tpm.
tpm(2)_clea from tpm(2)_utils should help

[PartialVolume]

If tpm2-tools is available in buildroot I'll add it into the next release.