board: toradex: apalis-imx8x: fix build instructions

Fix an URL for downloading the SCFW binary for an Apalis iMX8X
and improve u-boot image build instructions.
Signed-off-by: NOleksandr Suvorov <oleksandr.suvorov@toradex.com>

doc/board/toradex/apalix-imx8x.rst

 .. SPDX-License-Identifier: GPL-2.0+
 
-Apalis iMX8X V1.1A Module
+Apalis iMX8X V1.1A Module (SoC NXP i.MX8QXP RevB)
 ==========================
 
 Quick Start
 -----------
 
-- Build the ARM trusted firmware binary
-- Get scfw_tcm.bin and ahab-container.img
+- Get and Build the ARM trusted firmware
+- Get System Controller firmware
+- Get SECO container
 - Build U-Boot
 - Load U-Boot binary using uuu
 - Flash U-Boot binary into the eMMC
 - Boot
 
+Note: builddir is U-Boot build directory (source directory for in-tree builds)
+
 Get and Build the ARM Trusted Firmware
 --------------------------------------
 
 .. code-block:: bash
 
-    $ git clone -b toradex_imx_5.4.24_2.1.0 http://git.toradex.com/cgit/imx-atf.git
-    $ cd imx-atf/
-    $ make PLAT=imx8qx bl31
+    $ cd $(builddir)
+    $ git clone -b toradex_imx_5.4.70_2.3.0 http://git.toradex.com/cgit/imx-atf.git
+    $ make PLAT=imx8qx bl31 -C imx-atf
+    $ cp imx-atf/build/imx8qx/release/bl31.bin $(builddir)
 
-Get scfw_tcm.bin and ahab-container.img
+Get System Controller firmware
 ---------------------------------------
 
 .. code-block:: bash
 
-    $ wget https://github.com/toradex/i.MX-System-Controller-Firmware/blob/master/src/scfw_export_mx8qx_b0/build_mx8qx_b0/mx8qx-apalis-scfw-tcm.bin
-    $ wget https://www.nxp.com/lgfiles/NMG/MAD/YOCTO/imx-seco-3.6.3.bin
-    $ chmod +x imx-seco-3.6.3.bin
-    $ ./imx-seco-3.6.3.bin
+    $ wget https://github.com/toradex/i.MX-System-Controller-Firmware/raw/master/src/scfw_export_mx8qx_b0/build_mx8qx_b0/mx8qx-apalis-scfw-tcm.bin
 
-Copy the following binaries to the U-Boot folder:
+Get SECO container
+---------------------------------------
 
 .. code-block:: bash
 
-    $ cp imx-atf/build/imx8qx/release/bl31.bin .
-    $ cp imx-seco-3.6.3/firmware/seco/mx8qxb0-ahab-container.img mx8qx-ahab-container.imx8_defconfig
+    $ wget https://www.nxp.com/lgfiles/NMG/MAD/YOCTO/imx-seco-3.7.4.bin
+    $ sh imx-seco-3.7.4.bin
+    $ cp imx-seco-3.7.4/firmware/seco/mx8qxb0-ahab-container.img $(builddir)/mx8qx-ahab-container.img
 
 Build U-Boot
 ------------
@@ -58,7 +61,7 @@ to your host and execute uuu:
 
 .. code-block:: bash
 
-    sudo ./uuu u-boot/u-boot-dtb.imx
+    sudo ./uuu $(builddir)/u-boot-dtb.imx
 
 Flash the U-Boot Binary into the eMMC
 -------------------------------------