ppc: Move mirror_hack to arch_global_data

Move this field into arch_global_data and tidy up.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/powerpc/include/asm/global_data.h b/arch/powerpc/include/asm/global_data.h
index 2d7be45..b9037c4 100644
--- a/arch/powerpc/include/asm/global_data.h
+++ b/arch/powerpc/include/asm/global_data.h
@@ -119,6 +119,9 @@
 #if defined(CONFIG_4xx)
 	u32 uart_clk;
 #endif /* CONFIG_4xx */
+#if defined(CONFIG_SYS_GT_6426x)
+	unsigned int mirror_hack[16];
+#endif
 };
 
 /*
@@ -148,9 +151,6 @@
 #ifdef CONFIG_PRE_CONSOLE_BUFFER
 	unsigned long	precon_buf_idx;	/* Pre-Console buffer index */
 #endif
-#if defined(CONFIG_SYS_GT_6426x)
-	unsigned int	mirror_hack[16];
-#endif
 #if defined(CONFIG_A3000)	|| \
     defined(CONFIG_HIDDEN_DRAGON)  || \
     defined(CONFIG_MUSENKI)	||  \