Hexagon (target/hexagon) Improve code gen for predicated HVX instructions

Hexagon (target/hexagon) Improve code gen for predicated HVX instructions

The following improvements are made for predicated HVX instructions
    During gen_commit_hvx, unconditionally move the "new" value into
        the dest
    Don't set slot_cancelled
    Remove runtime bookkeeping of which registers were updated
    Reduce the cases where gen_log_vreg_write[_pair] is called
        It's only needed for special operands VxxV and VyV
    Remove gen_log_qreg_write

Signed-off-by: Taylor Simpson <tsimpson@quicinc.com>
Reviewed-by: Anton Johansson <anjo@rev.ng>
Message-Id: <20230307025828.1612809-15-tsimpson@quicinc.com>