arm/dts: OMAP3: Add omap3evm and am335xevm support

TI's OMAP3EVM and AM335xEVM are software development boards
available for OMAP35x(AM/DM37x) and AM335x devices respectively;
and these devices are considered under omap3 family.
Signed-off-by: NVaibhav Hiremath <hvaibhav@ti.com>
Cc: Benoit Cousson <b-cousson@ti.com>
Cc: Grant Likely <grant.likely@secretlab.ca>
Cc: Tony Lindgren <tony@atomide.com>
Signed-off-by: NGrant Likely <grant.likely@secretlab.ca>

Documentation/devicetree/bindings/arm/omap/omap.txt

@@ -41,3 +41,9 @@ Boards:
 
 - OMAP4 PandaBoard : Low cost community board
   compatible = "ti,omap4-panda", "ti,omap4430"
+
+- OMAP3 EVM : Software Developement Board for OMAP35x, AM/DM37x
+  compatible = "ti,omap3-evm", "ti,omap3"
+
+- AM335X EVM : Software Developement Board for AM335x
+  compatible = "ti,am335x-evm", "ti,am33xx", "ti,omap3"