efidebug: add multiple device path instances on Boot####

The UEFI spec allows a packed array of UEFI device paths in the
FilePathList[] of an EFI_LOAD_OPTION. The first file path must
describe the loaded image but the rest are OS specific.

Previous patches parse the device path and try to use the second
member of the array as an initrd. So let's modify efidebug slightly
and install the second file described in the command line as the
initrd device path.

Signed-off-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>