Add setexpr command

Add a simple expr style command that will set an env variable as the result
of the command.  This allows us to do simple math in shell.  The following
operations are supported: &, |, ^, +, -, *, /.

Signed-off-by: Kumar Gala <galak@kernel.crashing.org>
diff --git a/include/config_cmd_all.h b/include/config_cmd_all.h
index f3965ef..69276a3 100644
--- a/include/config_cmd_all.h
+++ b/include/config_cmd_all.h
@@ -70,6 +70,7 @@
 #define CONFIG_CMD_SAVES	/* save S record dump		*/
 #define CONFIG_CMD_SCSI		/* SCSI Support			*/
 #define CONFIG_CMD_SDRAM	/* SDRAM DIMM SPD info printout */
+#define CONFIG_CMD_SETEXPR	/* setexpr support 		*/
 #define CONFIG_CMD_SETGETDCR	/* DCR support on 4xx		*/
 #define CONFIG_CMD_SNTP		/* SNTP support			*/
 #define CONFIG_CMD_SPI		/* SPI utility			*/