VNNI pack: use linalg.generic instead of tpp.brgemm

[chelini]

To retire TPP we need to adjust VNNI packing to emit a linalg.generic instead of a tpp.brgemm:

tpp-mlir/lib/TPP/Transforms/ToBlockLayoutAndBack.cpp

Line 505 in 3e5bd37

auto replacementOp = rewriter.create<tpp::BrgemmOp>(