arm: remove prototype for get_timer_masked

The interruption support had be removed for ARM architecture and
the function get_timer_masked() is no more used except in some
the timer.c files.

This patch clean each timer.c which implement this function and
remove the associated prototype in u-boot-arm.h

For timer.c, I don't verify if the weak version of get_timer
(in lib/time.c) can be used

Signed-off-by: Patrick Delaunay <patrick.delaunay@st.com>
diff --git a/arch/arm/mach-imx/syscounter.c b/arch/arm/mach-imx/syscounter.c
index 676bb3c..34bdb95 100644
--- a/arch/arm/mach-imx/syscounter.c
+++ b/arch/arm/mach-imx/syscounter.c
@@ -89,14 +89,9 @@
 	return now;
 }
 
-ulong get_timer_masked(void)
-{
-	return tick_to_time(get_ticks());
-}
-
 ulong get_timer(ulong base)
 {
-	return get_timer_masked() - base;
+	return tick_to_time(get_ticks()) - base;
 }
 
 void __udelay(unsigned long usec)