tpm2_lite: use null password authorization for ReadLock
tpm2_lite: use null password authorization for ReadLock

Most of the indexes used in practice, have AUTHREAD set with null
password authentication. The only index, for which READ_STCLEAR is
set and TlclReadLock() is called is the one used by mount-encrypted.
It has AUTHREAD with empty password and should be lockable after
platform hierarchy is disabled. So, use null password authorization
instead of platform authorization in TlclReadLock().

BUG=chrome-os-partner:54708
BRANCH=none
TEST=Start with OOBE, corporate enroll, reboot, verify that the system
     doesn't go back to OOBE. Check mount-encrypted.log on start: it
     should contain "Read-locking NVRAM area succeeded".

Change-Id: Iaac78ba4dd048edac992adfab6fb94b69b2e989a
Reviewed-on: https://chromium-review.googlesource.com/410780
Commit-Ready: Andrey Pronin <53bbebe6910b11f7aa2d1daaa466658eb4cba5f2@chromium.org>
Tested-by: Andrey Pronin <53bbebe6910b11f7aa2d1daaa466658eb4cba5f2@chromium.org>
Reviewed-by: Vadim Bendebury <5515d6d2d0829cbe0dd0dcf2094aaded06d58514@chromium.org>

coreboot/vboot,coreboot/vboot,coreboot/vboot,coreboot/vboot,coreboot/vboot