m68k: powerpc: Clean up do_mdm_init

This code seems unnecessarily complex. We really just need to check the
global_data. Now that is it all in one place, and not arch-specific, this
is pretty easy.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/common/main.c b/common/main.c
index c4ed846..e3e9f84 100644
--- a/common/main.c
+++ b/common/main.c
@@ -14,17 +14,14 @@
 #include <malloc.h>
 #include <version.h>
 
+DECLARE_GLOBAL_DATA_PTR;
+
 /*
  * Board-specific Platform code can reimplement show_boot_progress () if needed
  */
 void inline __show_boot_progress (int val) {}
 void show_boot_progress (int val) __attribute__((weak, alias("__show_boot_progress")));
 
-#ifdef CONFIG_MODEM_SUPPORT
-int do_mdm_init = 0;
-extern void mdm_init(void); /* defined in board.c */
-#endif
-
 void main_loop(void)
 {
 #ifdef CONFIG_PREBOOT
@@ -40,8 +37,8 @@
 #endif
 
 #ifdef CONFIG_MODEM_SUPPORT
-	debug("DEBUG: main_loop:   do_mdm_init=%d\n", do_mdm_init);
-	if (do_mdm_init) {
+	debug("DEBUG: main_loop:   gd->do_mdm_init=%lu\n", gd->do_mdm_init);
+	if (gd->do_mdm_init) {
 		char *str = strdup(getenv("mdm_cmd"));
 		setenv("preboot", str);  /* set or delete definition */
 		if (str != NULL)