treewide: Apply nonstring attribute to unterminated strings

Applying the attribute silences the following error and allows
compilation with GCC 15.2.

  error: initializer-string for array of 'char' truncates NUL terminator but destination lacks 'nonstring' attribute

Change-Id: I33cf3219f34e297de03f67d3e73058b10930c9f8
Signed-off-by: Felix Singer <felixsinger@posteo.net>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/90631
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Maximilian Brune <maximilian.brune@9elements.com>

src/include/cpu/intel/smm_reloc.h

@@ -28,7 +28,7 @@ struct smm_relocation_params {
 extern struct smm_relocation_params smm_reloc_params;
 
 struct ied_header {
-	char signature[10];
+	char __nonstring signature[10];
 	u32 size;
 	u8 reserved[34];
 } __packed;