efi_loader: use proper device-paths for partitions

efi_loader: use proper device-paths for partitions

Also, create disk objects for the disk itself, in addition to the
partitions.  (UEFI terminology is a bit confusing, a "disk" object is
really a partition.)  This helps grub properly identify the boot device
since it is trying to match up partition "disk" object with it's parent
device.

Now instead of seeing devices like:

  /File(sdhci@07864000.blk)/EndEntire
  /File(usb_mass_storage.lun0)/EndEntire

You see:

  /ACPI(133741d0,0)/UnknownMessaging(1d)/EndEntire
  /ACPI(133741d0,0)/UnknownMessaging(1d)/HD(0,800,64000,dd904a8c00000000,1,1)/EndEntire
  /ACPI(133741d0,0)/UnknownMessaging(1d)/HD(1,64800,200000,dd904a8c00000000,1,1)/EndEntire
  /ACPI(133741d0,0)/UnknownMessaging(1d)/HD(2,264800,19a000,dd904a8c00000000,1,1)/EndEntire
  /ACPI(133741d0,0)/USB(0,0)/USB(0,0)/USB(0,0)/EndEntire
  /ACPI(133741d0,0)/USB(0,0)/USB(0,0)/USB(0,0)/HD(0,800,60000,38ca680200000000,1,1)/EndEntire
  /ACPI(133741d0,0)/USB(0,0)/USB(0,0)/USB(0,0)/HD(1,61000,155000,38ca680200000000,1,1)/EndEntire
  /ACPI(133741d0,0)/USB(0,0)/USB(0,0)/USB(0,0)/HD(2,20fa800,1bbf8800,38ca680200000000,1,1)/EndEntire
  /ACPI(133741d0,0)/USB(0,0)/USB(0,0)/USB(0,0)/HD(3,1b6800,1f44000,38ca680200000000,1,1)/EndEntire

This is on a board with single USB disk and single sd-card.  The
UnknownMessaging(1d) node in the device-path is the MMC device,
but grub_efi_print_device_path() hasn't been updated yet for some
of the newer device-path sub-types.

This patch is inspired by a patch originally from Peter Jones, but
re-worked to use efi_device_path, so it doesn't much resemble the
original.

Signed-off-by: Rob Clark <robdclark@gmail.com>
[agraf: s/unsigned/unsigned int/]
Signed-off-by: Alexander Graf <agraf@suse.de>