uboot-imx

test: env: Add test framework for env

Add a new "env" subcommand to the ut command.

This will run unit tests on the env code. This should be targetable to
any device that supports the env features needed for the tests.

Signed-off-by: Joe Hershberger <joe.hershberger@ni.com>
Reviewed-by: Simon Glass <sjg@chromium.org>