tpm: add stubs

tpm: add stubs

Commit c37cacabf22 moved tpm_cleanup() in the main loop exit, however this
function is not available when compiling with --disable-tpm.

Provides necessary stubs to keep code clean of #ifdef'fery.

Reported-by: BALATON Zoltan <[email protected]>
Message-Id: <20171023102903.256AF7456A0@zero.eik.bme.hu>
Signed-off-by: Philippe Mathieu-Daudé <[email protected]>
Tested-by: Richard W.M. Jones <[email protected]>
Reviewed-by: Juan Quintela <[email protected]>
Signed-off-by: Stefan Berger <[email protected]>