vboot: Only execute TPM clear on nonchrome FW

Prevent devices that are running ChromeOS FW from executing
a TPM clear request (designed for Flex), as it does not have
the HW to do so.

BUG=b:328654919
BRANCH=none
TEST=Deploy new changes to a flex liveboot and run the installer
     on a cb

Signed-off-by: Nehemiah Dureus <ndureus@chromium.org>
Change-Id: Ia50d9065edaf1d398ce58bd6e189d9cac7eda38d
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/vboot_reference/+/5656183
Reviewed-by: Julius Werner <jwerner@chromium.org>
Reviewed-by: Yi Chou <yich@google.com>