target-i386: kvm_check_features_against_host(): Use feature_word_info
Instead of carrying the CPUID leaf/register and feature name array on
the model_features_t struct, move that information into
feature_word_info so it can be reused by other functions.
The goal is to eventually kill model_features_t entirely, but to do that
we have to either convert x86_def_t.features to an array or use
offsetof() inside FeatureWordInfo (to replace the pointers inside
model_features_t). So by now just move most of the model_features_t
fields to FeatureWordInfo except for the two pointers to local
arguments.