cmd: Move CONFIG_RANDOM_UUID to Kconfig

CONFIG_RANDOM_UUID is used by the GPT command to generate random UUID when
none are provided.

Move that option to Kconfig.

Reviewed-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Jagan Teki <jagan@openedev.com>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>