lsefisystab: Add support for device tree table

lsefisystab: Add support for device tree table

The device tree may passed by the firmware as UEFI configuration
table. Let lsefisystab display a short text and not only the GUID
for the device tree.

Here is an example output:

  grub> lsefisystab
  Address: 0xbff694d8
  Signature: 5453595320494249 revision: 00020046
  Vendor: Das U-Boot, Version=20190700
  2 tables:
  0xbe741000  eb9d2d31-2d88-11d3-9a160090273fc14d   SMBIOS
  0x87f00000  b1b621d5-f19c-41a5-830bd9152c69aae0   DEVICE TREE

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>