Convert CONFIG_CMD_REISER to Kconfig

This converts the following to Kconfig:
   CONFIG_CMD_REISER

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
diff --git a/configs/ethernut5_defconfig b/configs/ethernut5_defconfig
index b9010d6..26df916 100644
--- a/configs/ethernut5_defconfig
+++ b/configs/ethernut5_defconfig
@@ -33,6 +33,7 @@
 CONFIG_CMD_EXT2=y
 CONFIG_CMD_FAT=y
 CONFIG_CMD_JFFS2=y
+CONFIG_CMD_REISER=y
 CONFIG_CMD_UBI=y
 CONFIG_OF_CONTROL=y
 CONFIG_DM=y