Function nclip 

pub fn nclip(
    vs2_elem: u64,
    shamt: u32,
    sew: Vsew,
    mode: Vxrm,
    vxsat: &mut bool,
) -> u64

Narrowing signed clip: read a 2*SEW signed element from vs2, shift right arithmetically with rounding, saturate to signed SEW range.

Same SEW constraint as nclipu.