target-i386: Simplify reporting of unavailable features

Instead of checking and calling unavailable_host_feature() once for each
bit, simply call the function (now renamed to
report_unavailable_features()) once for each feature word.

Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
[AF: Drop unused return value]
Signed-off-by: Andreas Färber <afaerber@suse.de>
