sandbox: Add 64-bit sandbox

To debug device tree issues involving 32- and 64-bit platforms, it is useful to
have a generic 64-bit platform available.

Add a version of the sandbox that uses 64-bit integers for its physical
addresses as well as a modified device tree.

Signed-off-by: Mario Six <mario.six@gdsys.cc>
Added CONFIG_SYS_TEXT_BASE to configs/sandbox64_defconfig
Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/board/sandbox/MAINTAINERS b/board/sandbox/MAINTAINERS
index 6d0790c..df29abe 100644
--- a/board/sandbox/MAINTAINERS
+++ b/board/sandbox/MAINTAINERS
@@ -5,6 +5,14 @@
 F:	include/configs/sandbox.h
 F:	configs/sandbox_defconfig
 
+SANDBOX64 BOARD
+M:	Simon Glass <sjg@chromium.org>
+M:	Mario Six <mario.six@gdsys.cc>
+S:	Maintained
+F:	board/sandbox/
+F:	include/configs/sandbox.h
+F:	configs/sandbox64_defconfig
+
 SANDBOX_NOBLK BOARD
 M:	Simon Glass <sjg@chromium.org>
 S:	Maintained