cs5535-clockevt: Allow the MFGPT IRQ to be shared

Shared timer IRQs are not a good solution, however the Geode platform has
no APIC, IRQs are a scarce resource and there is no technical reason to
forbid it rightaway.  Increased latencies and overhead due to sharing are
still better than a driver refusing to load.

Signed-off-by: Jens Rottmann <JRottmann@LiPPERTEmbedded.de>
Acked-by: Andres Salomon <dilinger@queued.net>
Cc: John Stultz <john.stultz@linaro.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>