Fuse RMS_NORM+MUL+ADD and ADD+ADD under GGML_SYCL_ENABLE_FUSION.
ADD+ADD uses the same binbcast indexing and type matrix as standalone
add() (f32, f16, f16/f32, i32, i16, bf16, including broadcast and
non-contiguous). Unsupported combinations fall back to two add() launches.