dm: usb: Deal with USB keyboard persisting across tests

Clear any USB-keyboard devices before running a unit test, to avoid
using a stale udevice pointer in stdio. Add a long comment to explain
this situation and why this solution seems best, at least for now.

Signed-off-by: Simon Glass <sjg@chromium.org>

common/console.c

@@ -1243,3 +1243,37 @@ int console_init_r(void)
 }
 
 #endif /* CONFIG_IS_ENABLED(SYS_CONSOLE_IS_IN_ENV) */
+
+int console_remove_by_name(const char *name)
+{
+	int err = 0;
+
+#if CONFIG_IS_ENABLED(CONSOLE_MUX)
+	int fnum;
+
+	log_debug("removing console device %s\n", name);
+	for (fnum = 0; fnum < MAX_FILES; fnum++) {
+		struct stdio_dev **src, **dest;
+		int i;
+
+		log_debug("file %d: %d devices: ", fnum, cd_count[fnum]);
+		src = console_devices[fnum];
+		dest = src;
+		for (i = 0; i < cd_count[fnum]; i++, src++) {
+			struct stdio_dev *sdev = *src;
+			int ret = 0;
+
+			if (!strcmp(sdev->name, name))
+				ret = stdio_deregister_dev(sdev, true);
+			else
+				*dest++ = *src;
+			if (ret && !err)
+				err = ret;
+		}
+		cd_count[fnum] = dest - console_devices[fnum];
+		log_debug("now %d\n", cd_count[fnum]);
+	}
+#endif /* CONSOLE_MUX */
+
+	return err;
+}