dt-bindings: add laird and giantec vendor prefix

This adds a vendor prefix "laird" for Laird PLC who make
CPU modules and system on chips.
Also adds "giantec" for Giantec Semiconductor, Inc. who
make eeprom memory used on Laird designs.

Signed-off-by: Ben Whitten <ben.whitten@lairdtech.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>