mx28evk: Add missing 'setexpr' command

The environment now uses expressions but we missed the setexpr command
was not being include. This patch adds it.

Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>
diff --git a/include/configs/mx28evk.h b/include/configs/mx28evk.h
index dffb744..7cdbec6 100644
--- a/include/configs/mx28evk.h
+++ b/include/configs/mx28evk.h
@@ -63,6 +63,7 @@
 #define CONFIG_CMD_NET
 #define CONFIG_CMD_NFS
 #define CONFIG_CMD_PING
+#define CONFIG_CMD_SETEXPR
 #define CONFIG_CMD_SF
 #define CONFIG_CMD_SPI
 #define CONFIG_CMD_USB