uboot-imx

test: ums: Add script for testing UMS gadget operation

This commit adds new test for UMS USB gadget to u-boot mainline tree.
It is similar in operation to the one already available in test/dfu
directory.

Signed-off-by: Lukasz Majewski <l.majewski@samsung.com>
Acked-by: Stephen Warren <swarren@nvidia.com>