[Ck tile] Use raw store to improve layernorm performance

[rocking5566]

Proposed changes

1. Simpler kernel example for layernorm
2. use store_tile_raw for Default2DEpilogueProblem to improve performance

Checklist

use following command to check performance make -j tile_layernorm2d_fwd && ./bin/tile_layernorm2d_fwd -m=128 -n=8192 -prec_i=bf16 -fadd=1