of: kunit: Extract some overlay boiler plate into macros

Make the lives of __of_overlay_apply_kunit() callers easier by
extracting some of the boiler plate involved in referencing the DT
overlays.

Cc: Brendan Higgins <[e-mail]>
Cc: David Gow <[e-mail]>
Cc: Rae Moar <[e-mail]>
Cc: Peng Fan <[e-mail]>
Signed-off-by: Stephen Boyd <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

include/kunit/of.h

···
 					  &unused);
 }
 
+#define of_overlay_begin(overlay_name) __dtbo_##overlay_name##_begin
+#define of_overlay_end(overlay_name) __dtbo_##overlay_name##_end
+
+#define OF_OVERLAY_DECLARE(overlay_name)			\
+	extern uint8_t of_overlay_begin(overlay_name)[];	\
+	extern uint8_t of_overlay_end(overlay_name)[]		\
+
 /**
  * of_overlay_apply_kunit() - Test managed of_overlay_fdt_apply() for built-in overlays
  * @test: test context
···
  */
 #define of_overlay_apply_kunit(test, overlay_name)		\
 ({								\
-	extern uint8_t __dtbo_##overlay_name##_begin[];		\
-	extern uint8_t __dtbo_##overlay_name##_end[];		\
+	OF_OVERLAY_DECLARE(overlay_name);			\
 								\
 	__of_overlay_apply_kunit((test),			\
-			__dtbo_##overlay_name##_begin,		\
-			__dtbo_##overlay_name##_end);		\
+			of_overlay_begin(overlay_name),		\
+			of_overlay_end(overlay_name));		\
 })
 
 #endif