x86: Permit bootstage and timer data to be used prior to relocation

It is useful to be able to access the timer before U-Boot has relocated
so that we can fully support bootstage.

Add new global_data members to support this.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/x86/cpu/interrupts.c b/arch/x86/cpu/interrupts.c
index dd30a05..6dc74e3 100644
--- a/arch/x86/cpu/interrupts.c
+++ b/arch/x86/cpu/interrupts.c
@@ -626,13 +626,12 @@
  */
 u64 get_ticks(void)
 {
-	static u64 tick_base;
 	u64 now_tick = rdtsc();
 
-	if (!tick_base)
-		tick_base = now_tick;
+	if (!gd->arch.tsc_base)
+		gd->arch.tsc_base = now_tick;
 
-	return now_tick - tick_base;
+	return now_tick - gd->arch.tsc_base;
 }
 
 #define PLATFORM_INFO_MSR 0xce