serial-dmm: Add support for Digitech QM1576 serial protocol parser

serial-dmm: Add support for Digitech QM1576 serial protocol parser

The protocol is described at https://www.airspayce.com/mikem/QM1578/protocol.txt

You can use this decoder with libsigrok and Digitech QM1578 via ESP32 Bluetooth-Serial converter available from the author at: https://www.airspayce.com/mikem/QM1578/QM1578BluetoothClient.ino which connects to the QM1578 over Bluetooth LE, fetches the data stream and sends it on the serial port to the host, where this driver can read it with this command for example:

sigrok-cli --driver digitech-qm1578:conn=/dev/ttyUSB1 --continuous