replace CONFIG_PRELOADER with CONFIG_SPL_BUILD

replace all occurences of CONFIG_PRELOADER with CONFIG_SPL_BUILD

Signed-off-by: Aneesh V <aneesh@ti.com>
diff --git a/README b/README
index ec66dc1..2cad44d 100644
--- a/README
+++ b/README
@@ -3075,7 +3075,7 @@
 		other boot loader or by a debugger which performs
 		these initializations itself.
 
-- CONFIG_PRELOADER
+- CONFIG_SPL_BUILD
 		Modifies the behaviour of start.S when compiling a loader
 		that is executed before the actual U-Boot. E.g. when
 		compiling a NAND SPL.