efi_selftest: dtbdump support EFI_DT_FIXUP_PROTOCOL

The dtbdump.efi binary can already be used to dump the configuration table
with the device-tree to a file.

With this patch a device-tree file can be loaded. The EFI_DT_FIXUP_PROTOCOL
is called to

* apply U-Boot's fix-ups
* let U-Boot make memory reservations as required by the device-tree
* install the new device-tree as configuration table

In a next step this configuration table can be dumped.

A dtbdump.efi session would look like:

    DTB Dump
    ========

    => load test.dtb
    device-tree installed
    => save fixed-up.dtb
    fixed-up.dtb written
    => exit

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>