patch 9.1.0109: filetype: no support for its files

patch 9.1.0109: filetype: no support for its files

Problem:  filetype: no support for its files
Solution: Add detection for *.its files as dts file type
          (Brandon Maier)

The '*.its' file type is for U-Boot Flattened Image Trees (FIT) which
use the flattened devicetree format.

See https://github.com/u-boot/u-boot/blob/master/doc/usage/fit/source_file_format.rst#terminology

closes: #14037

Signed-off-by: Brandon Maier <brandon.maier@collins.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>