ARM: OMAP: Fixes for RMK's comments and changed GPIO triggering

These fixes are based on RMK's comments here:

http://www.arm.linux.org.uk/developer/patches/viewpatch.php?id=2879/1

- BSS is zeroed, no reason to initialize variables in that area

- Made gpio.c use __void iomem *reg; instead of casting

- Made gpio triggering to set IRQT_NOEDGE at omap_request_gpio().
  The edge must be set with set_irq_type _after_ request_irq()