Hexagon HVX (target/hexagon) add Hexagon Vector eXtensions (HVX) to core

Hexagon HVX (target/hexagon) add Hexagon Vector eXtensions (HVX) to core

HVX is a set of wide vector instructions.  Machine state includes
    vector registers (VRegs)
    vector predicate registers (QRegs)
    temporary registers for intermediate values
    store buffer (masked stores and scatter/gather)

Acked-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Taylor Simpson <tsimpson@quicinc.com>