q35: remove duplicate initialization when initializing vtd

In mch_init_dmar(), remove the call to object_initialize() because
the initialization is done in object_new().

Signed-off-by: Le Tan <tamlokveer@gmail.com>
intel-iommu: change the way to maintain the array of address spaces in intel_iommu_state

Now intel_iommu_state.address_spaces is an array indexed by bus number, whose
elements each points to a table (initialized when needed). The table contains
pointers to vtd_address_space (initialized when needed), indexed by devfn.
This is an optimized method than before in saving memory space.

Signed-off-by: Le Tan <tamlokveer@gmail.com>