lower broadcast<type>x<vector> to shuffles.
there are two cases:
- src is 128 bits and dest is 512 bits: in this case we will lower it to shuffle with imm = 0.
- src is 256 bit and dest is 512 bits: in this case we will lower it to shuffle with imm = 01000100b (0x44) that way we will broadcast the 256bit source: ymm[0,1,2,3] => zmm[0,1,2,3,0,1,2,3] then it will mask it with the pass thru value (in case it's mask op).
Could you, please, change name to BRCST_SUBVEC_TO_VEC.