MLK-20061-2: doc: imx: Remove old encrypted_boot.txt documentation file

Signed-off-by: Clement Le Marquis <clement.lemarquis@nxp.com>

doc/imx/hab/habv4/encrypted_boot.txt

@@ -1,43 +0,0 @@
-1. Setup U-Boot Image for Encrypted Boot
-----------------------------------------
-An authenticated U-Boot image is used as starting point for
-Encrypted Boot. The image is encrypted by i.MX Code Signing
-Tool (CST). The CST replaces only the image data of
-u-boot-dtb.imx with the encrypted data. The Initial Vector Table,
-DCD, and Boot data, remains in plaintext.
-
-The image data is encrypted with a Encryption Key (DEK).
-Therefore, this key is needed to decrypt the data during the
-booting process. The DEK is protected by wrapping it in a Blob,
-which needs to be appended to the U-Boot image and specified in
-the CSF file.
-
-The DEK blob is generated by an authenticated U-Boot image with
-the dek_blob cmd enabled. The image used for DEK blob generation
-needs to have the following configurations enabled in Kconfig:
-
-CONFIG_SECURE_BOOT=y
-CONFIG_CMD_DEKBLOB=y
-
-Note: The encrypted boot feature is only supported by HABv4 or
-greater.
-
-The dek_blob command then can be used to generate the DEK blob of
-a DEK previously loaded in memory. The command is used as follows:
-
-dek_blob <DEK address> <Output Address> <Key Size in Bits>
-example: dek_blob 0x10800000 0x10801000 192
-
-The resulting DEK blob then is used to construct the encrypted
-U-Boot image. Note that the blob needs to be transferred back
-to the host.Then the following commands are used to construct
-the final image.
-
-cat u-boot-dtb.imx csf-u-boot.bin > u-boot-signed.imx
-objcopy -I binary -O binary --pad-to <blob_dst> --gap-fill=0x00 \
-    u-boot-signed.imx u-boot-signed-pad.bin
-cat u-boot-signed-pad.imx DEK_blob.bin > u-boot-encrypted.imx
-
-    NOTE: u-boot-signed.bin needs to be padded to the value
-    equivalent to the address in which the DEK blob is specified
-    in the CSF.