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/configs/sandbox_defconfig b/configs/sandbox_defconfig
index d50ce91..eba7bcb 100644
--- a/configs/sandbox_defconfig
+++ b/configs/sandbox_defconfig
@@ -315,6 +315,7 @@
 CONFIG_WDT_SANDBOX=y
 CONFIG_FS_CBFS=y
 CONFIG_FS_CRAMFS=y
+CONFIG_ADDR_MAP=y
 CONFIG_CMD_DHRYSTONE=y
 CONFIG_ECDSA=y
 CONFIG_ECDSA_VERIFY=y