ARM: omap3: evm: Name this directory omap3evm

Before this was named just evm, which doesn't match the naming
of the other TI board file directory and makes it look like a
common directory for evms. Name this omap3evm.

Signed-off-by: Andrew Davis <afd@ti.com>
Reviewed-by: Derald Woods <woods.technical@gmail.com>