ARM: omap3: evm: Enable DM_USB in defconfig

This addresses the following warning message:

===================== WARNING ======================
This board does not use CONFIG_DM_USB. Please update
the board to use CONFIG_DM_USB before the v2019.07 release.
Failure to update by the deadline may result in board removal.
See doc/driver-model/MIGRATION.txt for more info.
====================================================

As USB support for older OMAP3 SoC's improves, OMAP3 EVM can be
readily adapted. There is some additional 'gpio-hog' support
needed to fully setup USB in a similar manner to Linux.

Signed-off-by: Derald D. Woods <woods.technical@gmail.com>