tpm: Move eventlog declarations to its own header

Reduce the size of tpm.h by moving eventlog declarations to a separate
header.

Signed-off-by: Thiebaud Weksteen <tweek@google.com>
Suggested-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Reviewed-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Tested-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>