Use APInt array when deserializing int4 data

Passing an APInt array helps avoid a failure only observed when
building and running in debug mode. This assert checks that the
storage data type of the array that has been passed matches
expected MLIR type.

Change-Id: Id6d28b7feeb924aa414610f005562fb53dae140e
Signed-off-by: Luke Hutton <luke.hutton@arm.com>
Signed-off-by: Davide Grohmann <davide.grohmann@arm.com>