target-i386: Use FeatureWord loop on filter_features_for_kvm()

Instead of open-coding the filtering code for each feature word, change
the existing code to use the feature_word_info array, that has exactly
the same CPUID eax/ecx/register values for each feature word.

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Andreas Färber <afaerber@suse.de>