This replaces the old VA_FEATURES method for specifying codecs.

These VA codecs are included in the image when the image has 'hwcodec'
in the IMAGE_FEATURES variable.

One can disable the VA features by redefining the IMAGE_FEATURES
variable in local.conf.

Signed-off-by: Nitin A Kamble <nitin.a.kamble@intel.com>
Signed-off-by: Tom Zanussi <tom.zanussi@intel.com>