* Get (mostly) rid of CFG_MONITOR_LEN definition; compute real length

instead CFG_MONITOR_LEN is now only used to determine  _at_compile_
  _time_  (!) if the environment is embedded within the U-Boot image,
  or in a separate flash sector.

* Cleanup CFG_DER #defines in config files (wd maintained only)

include/common.h

@@ -128,6 +128,7 @@ int	checkflash    (void);
 int	checkdram     (void);
 char *	strmhz(char *buf, long hz);
 int	last_stage_init(void);
+extern ulong monitor_flash_len;
 
 /* common/flash.c */
 void flash_perror (int);