sandbox: Set up global_data earlier

It is possible for U-Boot functions such as printf() to be called
within state_init(). This can end up checking gd->flags (e.g. in putc())
before global_data is set up.

Move the setup earlier to avoid this. This fixes the suppression of some
debug output in memory allocation (when enabled).

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/sandbox/cpu/start.c b/arch/sandbox/cpu/start.c
index dce8041..0920ed5 100644
--- a/arch/sandbox/cpu/start.c
+++ b/arch/sandbox/cpu/start.c
@@ -483,6 +483,9 @@
 
 	text_base = os_find_text_base();
 
+	memset(&data, '\0', sizeof(data));
+	gd = &data;
+
 	/*
 	 * This must be the first invocation of os_malloc() to have
 	 * state->ram_buf in the low 4 GiB.
@@ -501,8 +504,6 @@
 		os_exit(1);
 	memcpy(os_argv, argv, size);
 
-	memset(&data, '\0', sizeof(data));
-	gd = &data;
 	gd->arch.text_base = text_base;
 
 	state = state_get_current();