doc: board: ti: Add missing firmware for BB-AI64

The details of the sysfw.itb from the R5 build that
also needs to be copied as part of the target images
is missing, but is included in the image formats a
little further down, so add it to the instructions.

Signed-off-by: Peter Robinson <pbrobinson@gmail.com>
Reviewed-by: Dhruva Gole <d-gole@ti.com>
Acked-by: Nishanth Menon <nm@ti.com>
diff --git a/doc/board/beagle/j721e_beagleboneai64.rst b/doc/board/beagle/j721e_beagleboneai64.rst
index 090b2b3..a57bc74 100644
--- a/doc/board/beagle/j721e_beagleboneai64.rst
+++ b/doc/board/beagle/j721e_beagleboneai64.rst
@@ -83,6 +83,7 @@
 Copy the below images to an SD card and boot:
 
 * tiboot3-j721e-gp-evm.bin from R5 build as tiboot3.bin
+* sysfw-j721e-gp-evm.itb from R5 build as sysfw.itb
 * tispl.bin_unsigned from Cortex-A build as tispl.bin
 * u-boot.img_unsigned from Cortex-A build as u-boot.img