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>

include/addr_map.h

@@ -14,7 +14,9 @@ struct addrmap {
 	unsigned long vaddr;
 };
 
+#ifdef CONFIG_ADDR_MAP
 extern struct addrmap address_map[CONFIG_SYS_NUM_ADDR_MAP];
+#endif
 
 phys_addr_t addrmap_virt_to_phys(void *vaddr);
 void *addrmap_phys_to_virt(phys_addr_t paddr);