[mlir][bufferization] Add specialized lowering for deallocs with one memref but arbitrary retains

It is often the case that many values in the `memrefs` operand list can be
split off to speparate dealloc operations by the
`--buffer-deallocation-simplification` pass, however, the retain list has to be
preserved initially. Further canonicalization can often trim it down
considerable, but some retains may remain. In those cases, the general lowering
would be chosen, but is very inefficient. This commit adds another lowering for
those cases which avoids allocation of auxillary memrefs and the helper
function while still producing code that is linear in the number of operands of
the dealloc operation.

Reviewed By: springerm

Differential Revision: https://reviews.llvm.org/D157692