cmd: efidebug: add uri device path

This adds the URI device path option for 'boot add' subcommand.
User can add the URI load option for downloading ISO image file
or EFI application through network. Currently HTTP is only supported.

Signed-off-by: Masahisa Kojima <masahisa.kojima@linaro.org>
Signed-off-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>