units: measure additional phases into PCR 11 when entering storage target mode or...

Let's "spoil" access to TPM secrets when we boot into these two modes.
This matters in particular for storagetm: if the host gets exploited
while booted into storage target mode any secrets kept by the TPM might
remain accessible otherwise. By measuring a new "phase" word into PCR 11
we "blow the fuse" however on this boot.