cmd: Add support for optee commands

cmd: Add support for optee commands

Add the basic 'hello world ta' command which increment
of the value passed. This provides easy test for
establishing a session with OP-TEE TA and verify.

It includes following "hello world ta" subcommands:
optee hello; default value '0' is passed and gets incremented.
optee hello <value>; value to increment via OP-TEE HELLO
WORLD TA.

To enable the OP-TEE side HELLO WORLD example please refer
https://optee.readthedocs.io/en/latest/building/gits/optee_examples/optee_examples.html

Signed-off-by: Venkatesh Yadav Abbarapu <venkatesh.abbarapu@amd.com>
Reviewed-by: Jerome Forissier <jerome.forissier@linaro.org>