tpm: Tie exclusive-open cleanup to the file lifetime

[kbowling]

Summary

Use a cdevpriv destructor to abort an unfinished TPM 1.2 transaction and
release exclusive-open ownership. Register it before setting TPM_OPEN so
a failed registration leaves the device available. The last reference to
the successful open triggers cleanup, including after dup() or fork().

Suggested by:   kevans
MFC after:      2 weeks