[mlir][Vector] Relax condition for `splitFullAndPartialTransferPrecondition`

The `splitFullAndPartialTransferPrecondition` has a restrictive condition to
prevent the pattern to be applied recursively if it is nested under an scf.IfOp.
Relaxing the condition to the immediate parent op must not be an scf.IfOp lets
the pattern be applied more generally while still preventing recursion.

Differential Revision: https://reviews.llvm.org/D85209