sandbox: make RAM size configurable

Up to now the RAM size of the sandbox is hard coded as 128 MiB. This does
not allow testing the correct handling of addresses outside the 32bit
range. 128 MiB is also rather small when tracing functions where the trace
is written to RAM.

Provide configuration variable CONFIG_SANDBOX_RAM_SIZE_MB to set the RAM
size in MiB. It defaults to 128 MiB with a minimum of 64 MiB.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/sandbox/include/asm/state.h b/arch/sandbox/include/asm/state.h
index 705645d..1bfad30 100644
--- a/arch/sandbox/include/asm/state.h
+++ b/arch/sandbox/include/asm/state.h
@@ -73,7 +73,7 @@
 	char **argv;			/* Command line arguments */
 	const char *jumped_fname;	/* Jumped from previous U_Boot */
 	uint8_t *ram_buf;		/* Emulated RAM buffer */
-	unsigned int ram_size;		/* Size of RAM buffer */
+	unsigned long ram_size;		/* Size of RAM buffer */
 	const char *ram_buf_fname;	/* Filename to use for RAM buffer */
 	bool ram_buf_rm;		/* Remove RAM buffer file after read */
 	bool write_ram_buf;		/* Write RAM buffer on exit */