Bootloaders: mention fs independent commands

fatload mmc ...
can be replaced by
load mmc ...

This works for fat, ext2, ext4...

Signed-off-by: Michael Opdenacker <michael.opdenacker@bootlin.com>

slides/sysdev-bootloaders-u-boot/sysdev-bootloaders-u-boot.tex

@@ -204,29 +204,31 @@ \subsection{The U-boot bootloader}
     \item And also \code{fatinfo}, \code{fatls}, \code{fatsize},
           \code{fatwrite}...
     \end{itemize}
-  \item \code{ext2load}, loads a file from an ext2 filesystem to RAM
+  \item Similar commands for other filesystems: \code{ext2load}, \code{ext2ls},
+      \code{ext4load}, \code{ext4ls}, \code{sqfsload}, \code{sqfsls}...
+      (\href{https://bootlin.com/blog/bootlin-contributes-squashfs-support-to-u-boot/}{SquashFS
+      support contributed by Bootlin})
+  \item Note that filesystem independent commands such as \code{load},
+        \code{ls}, and \code{size} exist. Examples:
     \begin{itemize}
-    \item And also \code{ext2info}, \code{ext2ls}, \code{ext2size},
-          \code{ext2write}...
+    \item \code{load usb 0:1 0x21000000 zImage}
+    \item \code{ls mmc 0:2 boot}
+    \item \code{size mmc 0:1 dtb} (result stored in \code{filesize} environment variable)
     \end{itemize}
-  \item Similar commands for other filesystems: \code{ext4load},
-      \code{ext4ls}, \code{sqfsload}, \code{sqfsls}...
-      (\href{https://bootlin.com/blog/bootlin-contributes-squashfs-support-to-u-boot/}{SquashFS
-      support contributed by Bootlin})...
+  \item \code{loadb}, \code{loads}, \code{loady}, load a file from the
+    serial line to RAM
   \item \code{tftp}, loads a file from the network to RAM (example given later)
-  \item \code{ping}, to test the network
-  \item \code{bootd} (can be abbreviated as \code{boot}), runs the default
-    boot command, stored in \code{bootcmd}
-  \item \code{bootz <address>}, starts a compressed kernel image loaded at the
-    given address in RAM
   \end{itemize}
 \end{frame}
 
 \begin{frame}
   \frametitle{Important commands (2)}
   \begin{itemize}
-  \item \code{loadb}, \code{loads}, \code{loady}, load a file from the
-    serial line to RAM
+  \item \code{ping}, to test the network
+  \item \code{bootd} (can be abbreviated as \code{boot}), runs the default
+    boot command, stored in \code{bootcmd}
+  \item \code{bootz <address>}, starts a compressed kernel image loaded at the
+    given address in RAM
   \item \code{usb}, to initialize and control the USB subsystem,
     mainly used for USB storage devices such as USB keys
   \item \code{mmc}, to initialize and control the MMC subsystem, used