target/mips: Switch to do_transaction_failed() hook

Switch the MIPS target from the old unassigned_access hook to the new
do_transaction_failed hook.

Unlike the old hook, do_transaction_failed is only ever called from
the TCG memory access paths, so there is no need for the "ignore this
if we're using KVM" hack that we were previously using to work around
the way unassigned_access was called for all kinds of memory accesses
to unassigned physical addresses.

The MIPS target does not ever do direct memory reads by physical
address (via either ldl_phys etc or address_space_ldl etc), so the
only memory accesses this affects are the 'normal' guest loads and
stores, which will be handled by the new hook; their behaviour is
unchanged.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Aleksandar Markovic <amarkovic@wavecomp.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Tested-by: Hervé Poussineau <hpoussin@reactos.org>
Message-Id: <20190802160458.25681-3-peter.maydell@linaro.org>