Make buffer hoisting/promotion passes use AllocationOpInterface

This update implements the usage of AllocationOpInterface in the buffer hoisting/promotion passes. Two interface methods, namely `getHoistingKind` and `buildPromotedAlloc`, have been added. The former indicates which kind of hoisting (loop, block) an allocation operation supports, while the latter builds a stack allocation operation for promotable allocations used by the promote-buffers-to-stack pass.

This update makes these passes be functional for user customized allocation operation.

Reviewed By: springerm

Differential Revision: https://reviews.llvm.org/D158398