scripts/dtc: dtx_diff - Show real file names in diff header

scripts/dtc: dtx_diff - Show real file names in diff header

PD#173147: update dtc to v1.4.4

As the comparison uses process substitution to pass files after
conversion to DTS format, the diff header doesn't show the real
filenames, but the names of the file descriptors used:

    --- /dev/fd/63  2017-06-22 11:21:47.531637188 +0200
    +++ /dev/fd/62  2017-06-22 11:21:47.531637188 +0200

This is especially annoying when comparing a bunch of DT files in a
loop, as the output doesn't show a clue about which files it refers to.

Fix this by explicitly passing the original file names to the diff
command using the --label option, giving e.g.:

    --- arch/arm/boot/dts/r8a7791-koelsch.dtb
    +++ arch/arm/boot/dts/r8a7791-porter.dtb

Change-Id: I6e070da490a8190682b7ec522e3f6746cdb651b2
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Frank Rowand <frank.rowand@sony.com>
Signed-off-by: Rob Herring <robh@kernel.org>