g: extension: Add a whitelist for vendor commands.

The USB FW upgrade endpoint should really only accept vendor commands
required to perform the firmware update.  This commit adds a whitelist
that is checked whenever a vendor command is received over this
endpoint.

The allowed commands over USB are the following:

 - EXTENSION_POST_RESET
 - VENDOR_CC_IMMEDIATE_RESET (only for dev images)

There is also functionality to have a whitelist for vendor commands that
come over the TPM interface.

BUG=chrome-os-partner:62815
BRANCH=None
TEST=Flash Cr50 with image containing this change.  Verify that an
upgrade over USB to newer image works.
TEST=Try using usb_updater to send a vendor command that's not in the
whitelist.  Verify that the vendor command is dropped.

Change-Id: I71f8ba090a1cc6c9e7c30ce0dd3c25259e8f292f
Signed-off-by: Aseda Aboagye <aaboagye@google.com>
Reviewed-on: https://chromium-review.googlesource.com/443447
Commit-Ready: Aseda Aboagye <aaboagye@chromium.org>
Tested-by: Aseda Aboagye <aaboagye@chromium.org>
Reviewed-by: Vadim Bendebury <vbendeb@chromium.org>
4 files changed