- add global config option ROOTLESS_X to control if enable
rootless X for the machine. ROOTLESS_X requires graphics
driver supporting KMS (kernel mode setting), so far, only
atom_pc support this. so enable ROOTLESS_X for atom_pc machine
- add config options for xf86-video-intel to support rootless X
Signed-off-by: Yu Ke <ke.yu@intel.com>