Changes

Create a gpu.module operation for the GPU Dialect.
Summary: This is based on the use of code constantly checking for an
attribute on a model and instead represents the distinct operaion with a
different op. Instead, this op can be used to provide better filtering.
Reverts "Revert "[mlir] Create a gpu.module operation for the GPU
Dialect.""
This reverts commit ac446302ca4145cdc89f377c0c364c29ee303be5 after 
fixing internal Google issues.
This additionally updates ROCDL lowering to use the new gpu.module.
Reviewers: herhut, mravishankar, antiagainst, nicolasvasilache
Subscribers: jholewinski, mgorny, mehdi_amini, jpienaar, burmako,
shauheen, csigg, arpith-jacob, mgester, lucyrfox, aartbik, liufengdb,
llvm-commits, mravishankar, rriddle, antiagainst, bkramer
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D72921