dt-bindings: vendor-prefixes: Add Vaisala

Vaisala Oyj is a company based in Finland and also has subsidiaries in other
countries. Vaisala develops, manufactures and markets innovative products and
services for environmental and industrial measurement.

https://www.vaisala.com/



Signed-off-by: Vesa Jääskeläinen <vesa.jaaskelainen@vaisala.com>
Signed-off-by: Rob Herring <robh@kernel.org>