fs: do_load: pass device path for efi payload

fatload command can be used to load the EFI payload since EFI system
partition is always a FAT partition. Call into EFI code from do_load()
to set the device path from which the last binary was loaded. An EFI
application like grub2 can’t find its configuration file without the
device path set.

Since device path is now set in do_load() there is no need to set it
in do_load_wrapper() for the load command.

Signed-off-by: Mian Yousaf Kaukab <ykaukab@suse.de>
Reviewed-by: Heinrich Schuchardt <xypron.glpk@gmx.de>