spl: Provide a way to mark code needed for relocation

Add a linker symbol which can be used to mark relocation code, so it can
be collected by the linker and copied into a suitable place and executed
when needed.

Signed-off-by: Simon Glass <sjg@chromium.org>

include/asm-generic/sections.h

@@ -67,6 +67,9 @@ extern char __text_start[];
 /* This marks the text region which must be relocated */
 extern char __image_copy_start[], __image_copy_end[];
 
+/* This marks the rcode region used for SPL relocation */
+extern char _rcode_start[], _rcode_end[];
+
 extern char __bss_end[];
 extern char __rel_dyn_start[], __rel_dyn_end[];
 extern char _image_binary_end[];
@@ -78,4 +81,17 @@ extern char __dtb[];
  */
 extern void _start(void);
 
+#ifndef USE_HOSTCC
+#if CONFIG_IS_ENABLED(RELOC_LOADER)
+#define __rcode __section(".text.rcode")
+#define __rdata __section(".text.rdata")
+#else
+#define __rcode
+#define __rdata
+#endif
+#else
+#define __rcode
+#define __rdata
+#endif
+
 #endif /* _ASM_GENERIC_SECTIONS_H_ */