malloc: Add 'malloc' command with 'info' subcommand

Add a command to display malloc heap statistics, showing total heap
size and memory currently in use.

Co-developed-by: Claude <noreply@anthropic.com>
Signed-off-by: Simon Glass <simon.glass@canonical.com>

doc/usage/cmd/malloc.rst

@@ -0,0 +1,45 @@
+.. SPDX-License-Identifier: GPL-2.0+:
+
+.. index::
+   single: malloc (command)
+
+malloc command
+==============
+
+Synopsis
+--------
+
+::
+
+    malloc info
+
+Description
+-----------
+
+The malloc command shows information about the malloc heap.
+
+info
+    Shows memory-allocation statistics, including the total heap size and the
+    amount currently in use.
+
+The total heap size is set by ``CONFIG_SYS_MALLOC_LEN``.
+
+Example
+-------
+
+::
+
+    => malloc info
+    total bytes  = 96 MiB
+    in use bytes = 700.9 KiB
+
+Configuration
+-------------
+
+The malloc command is enabled by CONFIG_CMD_MALLOC which depends on
+CONFIG_MALLOC_DEBUG.
+
+Return value
+------------
+
+The return value $? is 0 (true) on success, 1 (false) on failure.

doc/usage/index.rst

@@ -97,6 +97,7 @@ Shell commands
    cmd/loadx
    cmd/loady
    cmd/luks
+   cmd/malloc
    cmd/meminfo
    cmd/mbr
    cmd/md