Command calls update_tftp() analogous to automatic update described
in doc/README.update.

Usage:
fitupd [addr]
        - run update from FIT image at addr
          or from tftp 'updatefile'

Signed-off-by: Andreas Pretzsch <apr@cn-eng.de>

Signed-off-by: Bartlomiej Sieka <tur@semihalf.com>

The auto-update feature allows to automatically download software updates
from a TFTP server and store them in Flash memory during boot. Updates are
contained in a FIT file and protected with SHA-1 checksum.

More detailed description can be found in doc/README.update.

Signed-off-by: Rafal Czubak <rcz@semihalf.com>
Signed-off-by: Bartlomiej Sieka <tur@semihalf.com>