usb_updater: when communicating over tpm treat upgrades differently
usb_updater: when communicating over tpm treat upgrades differently

All extension and vendor commands' payloads need to be passed to the
processing functions the same way, whether they arrive over /dev/tpm0
or over USB. The upgrade PDUs sent over USB need to include two
additional fields which are stripped off by the reassembly layer on
the Cr50.

This patch makes sure that none of other than EXTENSION_FW_UPGRADE
commands sent over /dev/tpm0 by usb_updater have the extra
encapsulation.

BRANCH=cr50
BUG=b:62106898
TEST=verified that updates work the same way over TPM and USB (which
     includes sending the 'turn_update_on' commands. Before this patch
     the turn_update_on command sent by usb_updater over TPM was not
     processed properly (the timeout value was wrong).

Change-Id: I3f4ab7330037f6eb1ce8bac7c63faa5d7c309c94
Signed-off-by: Vadim Bendebury <5515d6d2d0829cbe0dd0dcf2094aaded06d58514@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/517416
Reviewed-by: Andrey Pronin <53bbebe6910b11f7aa2d1daaa466658eb4cba5f2@chromium.org>

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec