x86: GEODE: MFGPT: Use "just-in-time" detection for the MFGPT timers

There isn't much value to always detecting the MFGPT timers on
Geode platforms; detection is only needed when something wants
to use the timers.  Move the detection code so that it gets
called the first time a timer is allocated.

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>