arm: dts: iot2050: Optionally embed OTP programming data into image

Use external blob otpcmd.bin to replace the 0xff filled OTP programming
command block to create a firmware image that provisions the OTP on
first boot. This otpcmd.bin is generated from the customer keys using
steps described in the meta-iot2050 integration layer for the device.

Based on original patch by Baocheng Su.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
diff --git a/doc/board/siemens/iot2050.rst b/doc/board/siemens/iot2050.rst
index 4e0925c..cb49a0e 100644
--- a/doc/board/siemens/iot2050.rst
+++ b/doc/board/siemens/iot2050.rst
@@ -27,6 +27,14 @@
  - seboot_pg1.bin
  - seboot_pg2.bin
 
+For building an image containing the OTP key provisioning data, below binary
+needs to be present in the build folder:
+
+ - otpcmd.bin
+
+Regarding how to generating this otpcmd.bin, please refer to:
+https://github.com/siemens/meta-iot2050/tree/master/recipes-bsp/secure-boot-otp-provisioning/files/make-otpcmd.sh
+
 Building
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