clocksource/drivers/dw_apb_timer: Inline apbt_readl and apbt_writel

It seems gcc can automatically inline apbt_writel() for us, but
apbt_real isn't inlined. This patch makes them inline to get a trivial
performance improvement: 4096 rounds of __apbt_read_clocksource() call
spend time on Marvell BG4CT platform:

 before the patch 1275240ns on average
 after the patch 1263240ns on average

so we get 1% performance improvement.
Signed-off-by: Jisheng Zhang <jszhang@marvell.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>

drivers/clocksource/dw_apb_timer.c

@@ -49,13 +49,13 @@ clocksource_to_dw_apb_clocksource(struct clocksource *cs)
 	return container_of(cs, struct dw_apb_clocksource, cs);
 }
 
-static u32 apbt_readl(struct dw_apb_timer *timer, unsigned long offs)
+static inline u32 apbt_readl(struct dw_apb_timer *timer, unsigned long offs)
 {
 	return readl(timer->base + offs);
 }
 
-static void apbt_writel(struct dw_apb_timer *timer, u32 val,
-		 unsigned long offs)
+static inline void apbt_writel(struct dw_apb_timer *timer, u32 val,
+			unsigned long offs)
 {
 	writel(val, timer->base + offs);
 }