[MLIR] Added test operations to replace linalg dependency for
BufferizeTests.

Summary:
Added test operations to replace the LinalgDialect dependency in tests
which use the buffer-deallocation, buffer-hoisting,
buffer-loop-hoisting, promote-buffers-to-stack,
buffer-placement-preparation-allowed-memref-resutls and
buffer-placement-preparation pass. Adapted the corresponding tests cases
and TestBufferPlacement.cpp.

Differential Revision: https://reviews.llvm.org/D90037