Integrate xconfig/add_LICENSE.txt

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Commit: seco-ne/tools/xconfig@28791fe4

LICENSE: Add Apache 2.0 license file

According to our company licensing policy for software the Yocto layers
should be licensed under the Apache 2.0 license.
Adapt the LICENSE-2.0.txt file from https://www.apache.org/licenses/LICENSE-2.0.txt
as described in the APPENDIX.

Add the license as LICENSE.txt file to the layer repository.

BCS 746-000657

Change-Id: I247b2eb004aea29a13059d6e64bb0bc3d06ee9fe

SRCREV.conf

@@ -7,7 +7,7 @@ SRCREV_pn-touchcal-conv = "1e8a19e459299c4a77de9b04a1828a79613d7eea"
 SRCREV_pn-gfxml2dto = "a6c91245d6ce82890a950ef95b339f34f36a58a3"
 SRCREV_pn-egalaxi2c = "eacee19fe2bf02c8a00e25eb4494390d03c3cedd"
 SRCREV_pn-gfplatdetect = "bf3dbf8dc1707c41efdf863c0d3762dd1a2005be"
-SRCREV_pn-xconfig = "56afeb74eb5672982584291ffb6e0008d3756080"
+SRCREV_pn-xconfig = "28791fe47a41e11ec5cd54f594255dae115665c6"
 SRCREV_pn-linux-guf = "46b3952e3b35b91088408cf4e607fcf781fe963f"
 SRCREV_pn-linux-imx-kuk = "6eac325df3391a9501d7a2fb8ef098f8928b9a60"
 SRCREV_pn-u-boot-imx = "cedbe2148f087d8fed93db26e5daee49d18113ad"