memory: let address_space_rw/ld*/st* run outside the BQL

memory: let address_space_rw/ld*/st* run outside the BQL

The MMIO case is further broken up in two cases: if the caller does not
hold the BQL on invocation, the unlocked one takes or avoids BQL depending
on the locking strategy of the target memory region and its coalesced
MMIO handling.  In this case, the caller should not hold _any_ lock
(a friendly suggestion which is disregarded by virtio-scsi-dataplane).

Signed-off-by: Jan Kiszka <[email protected]>
Cc: Frederic Konrad <[email protected]>
Message-Id: <1434646046[email protected]>
Signed-off-by: Paolo Bonzini <[email protected]>