arch/arm/mach-mmp/: some files include some headers twice

arch/arm/mach-mmp/: some files include some headers twice:
- arch/arm/mach-mmp/aspenite.c and
  arch/arm/mach-mmp/tavorevb.c: 'linux/gpio.h'
- arch/arm/mach-mmp/pxa168.c: 'linux/platform_device.h'

Remove the duplicates.

Signed-off-by: Danny Kukawka <danny.kukawka@bisect.de>
Signed-off-by: Haojian Zhuang <haojian.zhuang@gmail.com>