[mlir][gpu] Add `gpu.binary` op and `#gpu.object` attribute.

**For an explanation of these patches see D154153.**

Commit message:
Adds the `#gpu.object` attribute for holding a binary object and the target
attribute used to create it. Also adds the `gpu.binary` operation used to
store GPU objects.

Depends on D154108

Reviewed By: mehdi_amini

Differential Revision: https://reviews.llvm.org/D154132