ivshmem: Simplify memory regions for BAR 2 (shared memory)

ivshmem: Simplify memory regions for BAR 2 (shared memory)

ivshmem_realize() puts the shared memory region in a container region.
Used to be necessary to permit delayed mapping of the shared memory.
However, we recently moved to synchronous mapping, in "ivshmem:
Receive shared memory synchronously in realize()" and the commit
following it.  The container is redundant since then.  Drop it.

Signed-off-by: Markus Armbruster <[email protected]>
Reviewed-by: Marc-André Lureau <[email protected]>
Reviewed-by: Paolo Bonzini <[email protected]>
Message-Id: <1458066895[email protected]>