Update details of Device-specific private key

This has been implemented for 2712 where there are now 16 rows.

Update the links because the script no longer lives in usbboot but comes
from rpi-eprom which is now a submodule in usbboot.

Fixes raspberrypi#3548

documentation/asciidoc/computers/raspberry-pi/raspberry-pi-industrial.adoc

@@ -161,9 +161,7 @@ If a customer MAC address is set to ff:ff:ff:ff:ff:ff, then it’s ignored.
 
 === Device-specific private key
 
-NOTE: This is not yet implemented for BCM2712 devices
-
-Eight rows of OTP (256 bits) are available for use as a device-specific private key. This is intended to support file-system encryption.
+Non-2712 devices have 8 rows of OTP (256 bits) available for use as a device-specific private key. On 2712 devices there are 16 rows of OTP data (512 bits). This is intended to support file-system encryption.
 
 These rows can be programmed and read using similar `vcmailbox` commands to those used for managing customer OTP rows. If
 secure-boot / file-system encryption is not required, then the device private key rows can be used to store general-purpose information.
@@ -175,11 +173,14 @@ secure-boot / file-system encryption is not required, then the device private ke
 See https://gitlab.com/cryptsetup/cryptsetup[Cryptsetup] for more information about open-source disk encryption.
 
 ==== Key programming script `rpi-otp-private-key`
-The https://github.com/raspberrypi/usbboot/blob/master/tools/rpi-otp-private-key[`rpi-otp-private-key`] script wraps the device private key `vcmailbox` APIs in order to make it easier to read/write a key in the same format as OpenSSL.
+The https://github.com/raspberrypi/rpi-eeprom/blob/master/tools/rpi-otp-private-key[`rpi-otp-private-key`] script wraps the device private key `vcmailbox` APIs in order to make it easier to read/write a key in the same format as OpenSSL.
+
+NOTE: The https://github.com/raspberrypi/usbboot[`usbboot`] repository contains all the tools you need and includes https://github.com/raspberrypi/rpi-eeprom[`rpi-eeprom`] as a git sub module.
 
-Read the key as a 64-byte hex number:
+Read the 32-byte key as a 64-character hex number:
 [,bash]
 ----
+cd usbboot/tools
 rpi-otp-private-key
 ----
 
@@ -188,13 +189,15 @@ Example output:
 f8dbc7b0a4fcfb1d706e298ac9d0485c2226ce8df7f7596ac77337bd09fbe160
 ----
 
-Writes a 64-byte randomly generated number to the device private key. +
+Writes a 32-byte randomly generated number to the device private key. +
 WARNING: This operation cannot be undone. 
 [,bash]
 ----
 # rpi-otp-private-key -w $(openssl rand -hex 32)
 ----
 
+NOTE: You can pass `-l <word count>` to specify the number of OTP rows to use and/or `-o <word offset>` to specify a start location in the key store.
+
 ==== Mailbox API for reading/writing the key.
 Read all of the rows.
 [,bash]