sandbox: Allow reading/writing of RAM buffer

It is useful to be able to save and restore the RAM contents of sandbox
U-Boot either for setting up tests, for later analysys, or for chaining
together multiple tests which need to keep the same memory contents.

Add a function to provide a memory file for U-Boot. This is read on
start-up and written when shutting down. If the file does not exist
on start-up, it will be created when shutting down.

Signed-off-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/sandbox/include/asm/global_data.h b/arch/sandbox/include/asm/global_data.h
index d70532a..b2e9b48 100644
--- a/arch/sandbox/include/asm/global_data.h
+++ b/arch/sandbox/include/asm/global_data.h
@@ -12,7 +12,7 @@
 
 /* Architecture-specific global data */
 struct arch_global_data {
-	u8		*ram_buf;	/* emulated RAM buffer */
+	uint8_t		*ram_buf;	/* emulated RAM buffer */
 };
 
 #include <asm-generic/global_data.h>