[HandshakeToDC] Allow pass to run in mixed dialect module

HandshakeToDC was trying to convert everything instead of just
`handshake.func`s and operations inside of them. Limit the conversion to
just things related to handshake.

lib/Conversion/HandshakeToDC/HandshakeToDC.cpp

@@ -819,8 +819,11 @@ LogicalResult circt::handshaketodc::runHandshakeToDC(
   // same type as the newly inserted operations). To do this, we mark all
   // operations which have been converted as legal, and all other operations
   // as illegal.
-  target.markUnknownOpDynamicallyLegal(
-      [&](Operation *op) { return convertedOps.contains(op); });
+  target.markUnknownOpDynamicallyLegal([&](Operation *op) {
+    return convertedOps.contains(op) ||
+           // Allow any ops which weren't in a `handshake.func` to pass through.
+           !convertedOps.contains(op->getParentOfType<hw::HWModuleOp>());
+  });
 
   DCTypeConverter typeConverter;
   RewritePatternSet patterns(ctx);

test/Conversion/HandshakeToDC/basic.mlir

@@ -261,3 +261,6 @@ hw.module @esi_outer(in %clk: !seq.clock, in %rst: i1, in %arg0: !esi.channel<i3
   %ret0, %ret1 = handshake.esi_instance @pack_unpack "pack_unpack_inst" clk %clk rst %rst (%arg0, %arg1) : (!esi.channel<i32>, !esi.channel<i1>) -> (!esi.channel<i32>, !esi.channel<i1>)
   hw.output %ret0 : !esi.channel<i32>
 }
+
+// CHECK: sv.verbatim "// Blah"
+sv.verbatim "// Blah"