x86: GEODE: make sure the right MFGPT timer fired the timer tick

Each AMD Geode MFGPT timer interrupt output is paired with another
timer; esentially the interrupt goes if either timer fires.  This
is okay, but the handlers need to be aware of this.  Make sure in
the timer tick handler that our timer really did expire.

Signed-off-by: Jordan Crouse <jordan.crouse@amd.com>
Signed-off-by: Andres Salomon <dilinger@debian.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>