UPSTREAM: timecounter: provide a macro to initialize the cyclecounter mask field.

(cherry picked from commit 1891172aa5c32f08ad9931b794edd71e91a4a527)

There is no need for users of the timecounter/cyclecounter code to include
clocksource.h just for a single macro.

Change-Id: I809b7690502d3c1fe397903432f0299803522e89
Signed-off-by: Richard Cochran <richardcochran@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>