va.h:Add new VAConfigAttribEncAutoReference
va.h:Add new VAConfigAttribEncAutoReference

Encoder usually has better knowledge about which
reference frame are the best one than application.

This attribute is used to signal application that
driver has this capability, and application doesn't
need to worry about reference frame settings

Signed-off-by: Austin Yuan <f447c34e4ebcef84a81b40a8d4dbc448a14e5570@intel.com>

halleyzhao/libva-fdo,CyanogenMod/android_hardware_intel_libva,CyanogenMod/android_hardware_intel_libva,android-ia/hardware_intel_libva,CyanogenMod/android_hardware_intel_libva,android-ia/hardware_intel_libva,halleyzhao/libva-fdo,android-ia/hardware_intel_libva,halleyzhao/libva-fdo