[mlir][linalg][bufferize] Remove remaining linalg dependencies

* Move "linalg.inplaceable" attr name literals to BufferizableOpInterface.
* Use `memref.copy` by default. Override to `linalg.copy` in ComprehensiveBufferizePass.

These are the last remaining code dependencies on Linalg in Comprehensive Bufferize. The next commit will make ComprehensiveBufferize independent of the Linalg dialect.

Differential Revision: https://reviews.llvm.org/D113457