efi_loader: support all uclasses in device path

On devices with multiple USB mass storage devices errors like

    Path /../USB(0x0,0x0)/USB(0x1,0x0)/Ctrl(0x0)
    already installed.

are seen. This is due to creating non-unique device paths. To uniquely
identify devices we must provide path nodes for all devices on the path
from the root device.

Add support for generating device path nodes for all uclasses.

Reported-by: Suniel Mahesh <sunil@amarulasolutions.com>
Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>