dt: add vendor prefix for EM Microelectronics

Add "emmicro" as the prefix for EM Microelectronics. A web search implies
this is a pretty unique and relevant match.
Signed-off-by: NStephen Warren <swarren@nvidia.com>
Signed-off-by: NGrant Likely <grant.likely@secretlab.ca>

Documentation/devicetree/bindings/vendor-prefixes.txt

@@ -13,6 +13,7 @@ chrp	Common Hardware Reference Platform
 cortina	Cortina Systems, Inc.
 dallas	Maxim Integrated Products (formerly Dallas Semiconductor)
 denx	Denx Software Engineering
+emmicro	EM Microelectronic
 epson	Seiko Epson Corp.
 est	ESTeem Wireless Modems
 fsl	Freescale Semiconductor