cmd: bootefi: rework set_load_options()

set_load_options() can fail, so it should return error code to stop
invoking an image.
In addition, set_load_options() now takes a handle, instead of
loaded_image_info, to utilize efi_load_image() in a later patch.

Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
Reviewed-by: Heinrich Schuchardt <xypron.glpk@gmx.de>