[tosa] Align with the custom assembly format change.
Kindly remind that https://reviews.llvm.org/D155231 has been merged, free feel to adopt this PR to match. @tatwaichong Thank you for the patch! This week, I'm on a Google-internal rotation that bumps LLVM versions, and this will help big time. I'll land this change internally, and it'll bubble up to tensorflow/tensorflow soon. Thanks your help. I've just rebased this PR and resolved the conflicts. Close this PR as the change has been merged in a LLVM integration.
Synchronize to the change in mlir.

link to the PR https://reviews.llvm.org/D155231.