labs/sysdev-u-boot-beagleplay: use absolute paths for ATF and DM make parameters

In the version of U-Boot used in this lab, the ATF and DM make parameters are
interpreted as relative to the build directory, and not the current directory.
This causes the build to produce broken images that contain neither TF-A nor
the DM firmware.

Fix this build command by passing ATF and DM as absolute paths instead of
relative ones.

Signed-off-by: Romain Gantois <[email protected]>

Author: rgantois

labs/sysdev-u-boot-beagleplay/sysdev-u-boot-beagleplay.tex

@@ -345,18 +345,18 @@ \section{Configure U-boot for the A53 Processor}
   to the makefile:
 
   \begin{itemize}
-  \item The path to the Trusted Firmware (TF-A):
-    \code{ATF=../arm-trusted-firmware/build/k3/lite/release/bl31.bin}
-  \item The path to the Device Management Firmware (DM) which is included
+  \item The absolute path to the Trusted Firmware (TF-A):
+    \code{ATF=$(realpath ../arm-trusted-firmware/build/k3/lite/release/bl31.bin)}
+  \item The absolute path to the Device Management Firmware (DM) which is included
     by the \code{ti-linux-firmware} package we downloaded before:
-    \code{DM=../ti-linux-firmware/ti-dm/am62xx/ipc_echo_testb_mcu1_0_release_strip.xer5f}
+    \code{DM=$(realpath ../ti-linux-firmware/ti-dm/am62xx/ipc_echo_testb_mcu1_0_release_strip.xer5f)}
   \item As usual, do not forget to specify the output directory:
     \code{O=../build_uboot/a53}
   \end{itemize}
 
   \begin{bashinput}
-$ make ATF=../arm-trusted-firmware/build/k3/lite/release/bl31.bin \
-    DM=../ti-linux-firmware/ti-dm/am62xx/ipc_echo_testb_mcu1_0_release_strip.xer5f \
+$ make ATF=$(realpath ../arm-trusted-firmware/build/k3/lite/release/bl31.bin) \
+    DM=$(realpath ../ti-linux-firmware/ti-dm/am62xx/ipc_echo_testb_mcu1_0_release_strip.xer5f) \
     O=../build_uboot/a53
   \end{bashinput}
 \end{enumerate}