blackfin: bf609: add softswitch config command

Add softswitch_output command for bf609-ezkit to enable softswitches.

Signed-off-by: Bob Liu <lliubbo@gmail.com>
Signed-off-by: Sonic Zhang <sonic.zhang@analog.com>
diff --git a/README b/README
index 0d37d56..defdedb 100644
--- a/README
+++ b/README
@@ -898,6 +898,7 @@
 		CONFIG_CMD_SF		* Read/write/erase SPI NOR flash
 		CONFIG_CMD_SHA1SUM	  print sha1 memory digest
 					  (requires CONFIG_CMD_MEMORY)
+		CONFIG_CMD_SOFTSWITCH	* Soft switch setting command for BF60x
 		CONFIG_CMD_SOURCE	  "source" command Support
 		CONFIG_CMD_SPI		* SPI serial bus support
 		CONFIG_CMD_TFTPSRV	* TFTP transfer in server mode