[BACKEND] Replace Func Dialect with custom triton ops (func, call, return) (#1502)

MLIR current only supports a custom inlining interface per dialect, so
we cannot change the inlining decision of `func.func`.


https://discourse.llvm.org/t/avoid-inlining-some-functions-using-the-func-dialect/69830/3

Could revert it back once they've designed a better inliner interface.

Inlining attributes will be implemented in the next PR since this PR is
already huge.

lib/Analysis/AxisInfo.cpp

@@ -77,7 +77,7 @@ AxisInfo AxisInfo::getPessimisticValueState(Value value) {
 
   if (blockArg && blockArg.getOwner()->isEntryBlock()) {
     Operation *op = blockArg.getOwner()->getParentOp();
-    if (auto fun = dyn_cast<func::FuncOp>(op))
+    if (auto fun = dyn_cast<triton::FuncOp>(op))
       initPessimisticStateFromFunc(blockArg.getArgNumber(), fun,
                                    &knownContiguity, &knownDivisibility,
                                    &knownConstancy);