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/arm1136/mx31/timer.c b/arch/arm/cpu/arm1136/mx31/timer.c
index 790bab4..b006b60 100644
--- a/arch/arm/cpu/arm1136/mx31/timer.c
+++ b/arch/arm/cpu/arm1136/mx31/timer.c
@@ -115,12 +115,12 @@
 {
 	ulong now = GPTCNT; /* current tick value */
 
-	if (now >= gd->lastinc)	/* normal mode (non roll) */
+	if (now >= gd->arch.lastinc)	/* normal mode (non roll) */
 		/* move stamp forward with absolut diff ticks */
-		gd->arch.tbl += (now - gd->lastinc);
+		gd->arch.tbl += (now - gd->arch.lastinc);
 	else			/* we have rollover of incrementer */
-		gd->arch.tbl += (0xFFFFFFFF - gd->lastinc) + now;
-	gd->lastinc = now;
+		gd->arch.tbl += (0xFFFFFFFF - gd->arch.lastinc) + now;
+	gd->arch.lastinc = now;
 	return gd->arch.tbl;
 }