Add clear TPM owner request

This adds two new flags to crossystem:
   clear_tpm_owner_request
   clear_tpm_owner_done

The first one requests that the firmware clear the TPM owner on the
next boot.  When the firmware does this, it will set
clear_tpm_owner_request=0, and set clear_tpm_owner_done=1.  The OS can
use the done-flag as a hint that trusted things guarded by the TPM are
no longer trustable.

BUG=chromium-os:31974
TEST=manual

crossystem
  // both flags initially 0
crossystem clear_tpm_owner_request=1
crossystem clear_tpm_owner_done=1
  // request=1, done=0; done can be cleared but not set by crossystem
reboot
tpmc getownership
  // owned=no
crossystem
  // request=0, done=1
crossystem clear_tpm_owner_done=0
crossystem
  // both flags 0 again

Signed-off-by: Randall Spangler <rspangler@chromium.org>
Change-Id: I49f83f3c39c3efc3945116c51a241d255c2e42cd
Reviewed-on: https://gerrit.chromium.org/gerrit/25646
12 files changed