rigol-ds: Fix #1831 by supporting DS1xxxZ Plus & RPL1116 logic ports

rigol-ds: Fix #1831 by supporting DS1xxxZ Plus & RPL1116 logic ports

The DS1xxxZ Plus models are MSO ready, they contain the connector to attach a RPL1116 16 port digital head.
Having a DS1xxxZ Plus and a connected RPL1116 effectively the instrument becomes a MSO1xxxZ.

But that "CH_INFO(4, false)" means 4 analog channels and NO digital channels.
As said though, the DS1xxxZ Plus variants got the D0..D15 digital ports abilities already so this line treats the DS1xxxZ Plus as a plain DS1xxxZ without the digital ports.

A very simple remedy is to change the CH_INFO(4, false) to CH_INFO(4, true)
So those two lines should be changed
from
{SERIES(DS1000Z), "DS1074Z Plus", {5, 1000000000}, CH_INFO(4, false), std_cmd},
{SERIES(DS1000Z), "DS1104Z Plus", {5, 1000000000}, CH_INFO(4, false), std_cmd},
to
{SERIES(DS1000Z), "DS1074Z Plus", {5, 1000000000}, CH_INFO(4, true), std_cmd},
{SERIES(DS1000Z), "DS1104Z Plus", {5, 1000000000}, CH_INFO(4, true), std_cmd},
and the problem will be solved.