We have recently had issues with older revisions of the Minnowboard
firmware, resulting in a 5 minute pause at boot (due to the addition of
reset attack mitigation functionality in newer versions of Linux).

We are in the process of updating boards to the latest firmware available.
Document the version that we are using and recommend that others update
their firmware.

Signed-off-by: Martyn Welch <martyn.welch@collabora.com>