Load option with short device path for boot vars

Load option with short device path for boot vars

The boot variables automatically generated for removable medias
should be with short form of device path without device nodes.
This is a requirement for the case that a removable media is
plugged into a different port but is still able to work with the
existing boot variables.

Signed-off-by: Raymond Mao <raymond.mao@linaro.org>
Reviewed-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>