[new uImage] Add proper ramdisk/FDT handling when FIT configuration is used

Save FIT configuration provied in the first bootm argument and use it
when to get ramdisk/FDT subimages when second and third (ramdisk/FDT)
arguments are not specified.

Signed-off-by: Marian Balakowicz <m8@semihalf.com>
diff --git a/README b/README
index 183246e..0ed47f0 100644
--- a/README
+++ b/README
@@ -1769,6 +1769,7 @@
  -101	common/cmd_bootm.c	Can't get configuration for kernel subimage
   102	common/cmd_bootm.c	Kernel unit name specified
  -103	common/cmd_bootm.c	Can't get kernel subimage node offset
+  103	common/cmd_bootm.c	Found configuration node
   104	common/cmd_bootm.c	Got kernel subimage node offset
  -104	common/cmd_bootm.c	Kernel subimage hash verification failed
   105	common/cmd_bootm.c	Kernel subimage hash verification OK