Introduce CONFIG_SPL_PANIC_ON_RAW_IMAGE

introduce CONFIG_SPL_PANIC_ON_RAW_IMAGE.
An SPL which define this will panic() if the
image it has loaded does not have a mkimage
signature.

Signed-off-by: Albert ARIBAUD (3ADEV) <albert.aribaud@3adev.fr>
diff --git a/README b/README
index b7c2a17..9b748cc 100644
--- a/README
+++ b/README
@@ -3607,6 +3607,16 @@
 		CONFIG_SPL_STACK
 		Adress of the start of the stack SPL will use
 
+		CONFIG_SPL_PANIC_ON_RAW_IMAGE
+		When defined, SPL will panic() if the image it has
+		loaded does not have a signature.
+		Defining this is useful when code which loads images
+		in SPL cannot guarantee that absolutely all read errors
+		will be caught.
+		An example is the LPC32XX MLC NAND driver, which will
+		consider that a completely unreadable NAND block is bad,
+		and thus should be skipped silently.
+
 		CONFIG_SPL_RELOC_STACK
 		Adress of the start of the stack SPL will use after
 		relocation.  If unspecified, this is equal to