clocksource/drivers/arc_timer: Use BIT() instead of _BITUL()

This is in-kernel C code, so there is no reason to use _BITUL().
Replace it with equivalent BIT().

I added #include <linux/bits.h> explicitly although it has been included
by other headers eventually.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>

drivers/clocksource/arc_timer.c

@@ -16,6 +16,7 @@
  */
 
 #include <linux/interrupt.h>
+#include <linux/bits.h>
 #include <linux/clk.h>
 #include <linux/clk-provider.h>
 #include <linux/clocksource.h>
@@ -142,7 +143,7 @@ static u64 arc_read_rtc(struct clocksource *cs)
 		l = read_aux_reg(AUX_RTC_LOW);
 		h = read_aux_reg(AUX_RTC_HIGH);
 		status = read_aux_reg(AUX_RTC_CTRL);
-	} while (!(status & _BITUL(31)));
+	} while (!(status & BIT(31)));
 
 	return (((u64)h) << 32) | l;
 }