sandbox: Support loading the other FDT

We need an 'other' FDT which is different from the control FDT, so we can
check that the ofnode tests correctly handle them both.

Add this to the build along with a way to read it into the sandbox state.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/sandbox/cpu/state.c b/arch/sandbox/cpu/state.c
index 787e021..fcc4a33 100644
--- a/arch/sandbox/cpu/state.c
+++ b/arch/sandbox/cpu/state.c
@@ -418,6 +418,32 @@
 	return len;
 }
 
+int state_load_other_fdt(const char **bufp, int *sizep)
+{
+	struct sandbox_state *state = state_get_current();
+	char fname[256];
+	int len, ret;
+
+	/* load the file if needed */
+	if (!state->other_fdt_buf) {
+		len = state_get_rel_filename("arch/sandbox/dts/other.dtb",
+					     fname, sizeof(fname));
+		if (len < 0)
+			return len;
+
+		ret = os_read_file(fname, &state->other_fdt_buf,
+				   &state->other_size);
+		if (ret) {
+			log_err("Cannot read file '%s'\n", fname);
+			return ret;
+		}
+	}
+	*bufp = state->other_fdt_buf;
+	*sizep = state->other_size;
+
+	return 0;
+}
+
 int state_init(void)
 {
 	state = &main_state;