devicetree: bindings: add Zarlink to the vendor prefixes

Even though the company belongs to Microsemi, many chips are still
labeled as Zarlink. Among them is the family of network clock generators,
the zl3034x.

Signed-off-by: Valentin Longchamp <valentin.longchamp@keymile.com>
Signed-off-by: Scott Wood <scottwood@freescale.com>