sandbox: Add sandbox board

This adds basic files for the sandbox board. The lds file is very simple
since we can rely mostly on the linker defaults.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/boards.cfg b/boards.cfg
index bd70a66..1e3bfdc 100644
--- a/boards.cfg
+++ b/boards.cfg
@@ -264,6 +264,7 @@
 tcm-bf537                    blackfin    blackfin
 eNET                         x86         x86        eNET                -              sc520       eNET:SYS_TEXT_BASE=0x38040000
 eNET_SRAM                    x86         x86        eNET                -              sc520       eNET:SYS_TEXT_BASE=0x19000000
+sandbox                      sandbox     sandbox     sandbox             sandbox        -
 idmr                         m68k        mcf52x2
 TASREG                       m68k        mcf52x2     tasreg              esd
 M5208EVBE                    m68k        mcf52x2     m5208evbe           freescale