target/i386/misc_helper: wrap BQL around another IRQ generator

Anything that calls into HW emulation must be protected by the BQL.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Richard Henderson <rth@twiddle.net>
Acked-by: Eduardo Habkost <ehabkost@redhat.com>
