* 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)

board/shannon/flash.c

@@ -124,7 +124,7 @@ ulong flash_init(void)
 #else
     flash_protect(FLAG_PROTECT_SET,
 		  CFG_FLASH_BASE,
-		  CFG_FLASH_BASE + _armboot_end_data - _armboot_start,
+		  CFG_FLASH_BASE + monitor_flash_len - 1,
 		  &flash_info[0]);
 
     flash_protect(FLAG_PROTECT_SET,