cmd: env: check real location for env info command

Check the current ENV location, dynamically provided by the weak
function env_get_location to be sure that the environment can be
persistent.

The compilation flag ENV_IS_IN_DEVICE is not enough when the board
dynamically select the available storage location (according boot
device for example).

This patch solves issue for stm32mp1 platform, when the boot device
is USB.

Signed-off-by: Patrick Delaunay <patrick.delaunay@st.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Tom Rini <trini@konsulko.com>