clocksource: Fix dependencies for archs w/o HAS_IOMEM

Not every arch has io memory.
So, unbreak the build by fixing the dependencies.

Signed-off-by: Richard Weinberger <richard@nod.at>
Cc: user-mode-linux-devel@lists.sourceforge.net
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: http://lkml.kernel.org/r/1453760661-1444-21-git-send-email-richard@nod.at
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>