linux-imx

OF/device-tree: Add some entries to vendor-prefixes.txt

We are currently using 'cavium', 'cortina' and 'st', add them to the
list of known prefixes.

Signed-off-by: David Daney <david.daney@cavium.com>
Signed-off-by: Rob Herring <rob.herring@calxeda.com>