IXP: add dynamic microcode addr

allow to load the microde from flash or ram by download it through
the serial or other.

Signed-off-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
Acked-by: Stefan Roese <sr@denx.de>
diff --git a/README b/README
index f2a4914..cc55274 100644
--- a/README
+++ b/README
@@ -2699,6 +2699,9 @@
 		  Useful on scripts which control the retry operation
 		  themselves.
 
+  npe_ucode	- see CONFIG_IXP4XX_NPE_EXT_UCOD
+		  if set load address for the npe microcode
+
   tftpsrcport	- If this is set, the value is used for TFTP's
 		  UDP source port.