arm: Move lastinc 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/arm/cpu/arm926ejs/omap/timer.c b/arch/arm/cpu/arm926ejs/omap/timer.c
index 71b8700..34ec7b2 100644
--- a/arch/arm/cpu/arm926ejs/omap/timer.c
+++ b/arch/arm/cpu/arm926ejs/omap/timer.c
@@ -45,7 +45,7 @@
 DECLARE_GLOBAL_DATA_PTR;
 
 #define timestamp gd->arch.tbl
-#define lastdec gd->lastinc
+#define lastdec gd->arch.lastinc
 
 int timer_init (void)
 {