OMAP3: clock: indicate that gpt12_fck and wdt1_fck are in the WKUP clockdomain

The oscillator that supplies GPT12_FCLK and WDT1_FCLK exists in the
WKUP powerdomain[1].  This resolves at least one boot-time warning:

omap_hwmod: gpt12_fck: missing clockdomain for gpt12_fck.

1. _OMAP34xx Multimedia High Security (HS) Device Silicon Revision 3.1.x
   Security Addendum Version K (SWPU119K)_  Figure 3-29.  August 2010.