target-i386: Support check/enforce flags in TCG mode, too

If enforce/check is specified in TCG mode, QEMU will ensure all CPU
features are supported by TCG, so no CPU feature is silently disabled.

Reviewed-by: Richard Henderson <rth@twiddle.net>
Signed-off-by: Eduardo Habkost <ehabkost@redhat.com>
[AF: Be explicit about TCG vs. !KVM]
Signed-off-by: Andreas Färber <afaerber@suse.de>
