addrmap: Support on sandbox

Update this feature so that it works on sandbox, using a basic identity
mapping. This allows us to run the 'ut addrmap' test.

Also fix up the test to use the correct macros to access the linker
list, so that the 'ut addrmap' command actually works.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/board/sandbox/sandbox.c b/board/sandbox/sandbox.c
index e054f30..ca9a2ca 100644
--- a/board/sandbox/sandbox.c
+++ b/board/sandbox/sandbox.c
@@ -4,6 +4,7 @@
  */
 
 #include <common.h>
+#include <addr_map.h>
 #include <cpu_func.h>
 #include <cros_ec.h>
 #include <dm.h>
@@ -155,3 +156,11 @@
 	return 0;
 }
 #endif
+
+int init_addr_map(void)
+{
+	if (IS_ENABLED(CONFIG_ADDR_MAP))
+		addrmap_set_entry(0, 0, CONFIG_SYS_SDRAM_SIZE, 0);
+
+	return 0;
+}