[Codegen][CPU] Drop the ACC stride from the inner_tiled ukernel ABI. (#24652)

New bottom of the LLVMCPU C-ukernel stack.

The ACC stride threaded to the C ukernels is always a compile-time
constant
equal to one intrinsic's ACC fragment size (the data-tiled ACC tile is
contiguous), so it folds to a constant after inlining and carries no
information the intrinsic-specific ukernel doesn't already encode. This
drops
it:

- `IREECPUAttrs.cpp`: remove `getAccInnermostCrossIntrinsicDim`; build
the
`ukernel.generic` with `num_strided_outer_dims=0`, so all shaped
operands
  (LHS, RHS, ACC) lower to `(base, offset)` only.
- Both seed ukernel `.c` signatures lose the `acc_stride` parameter.

This addresses review feedback on the now-merged #24569 / #24571 (why
pass a
per-operand `strided_dims` array, and why pass an ACC stride that's
statically
known). It makes the three operands uniform and removes the
`getAccInnermostCrossIntrinsicDim` swizzle machinery.

Verified: the lowered `llvm.call` to the ukernel now has no stride
argument,
and the ukernel lit tests (`lower_inner_tiled_to_bitcode_ukernel*`,
`e2e_inner_tiled_pipeline`, `select_ukernel`) pass.

Progress towards https://github.com/iree-org/iree/issues/24574.

Signed-off-by: Benoit Jacob <jacob.benoit.1@gmail.com>