serial-dmm: add EEVblog 121GW device entry (-d eevblog-121gw:conn=<uart>)

Add an "eevblog-121gw" subdriver entry for the EEVblog 121GW multimeter.
Use device dependent channel names instead of the default "P1" etc names.

It's assumed that the device's binary packet data is available at a COM
port. This means that an external BT to UART gateway is required until
BLE communication will be one of libsigrok's native connection types.
2 files changed