device: Fix leak if probe groups are created.
serial: Fix leak in serial_open.

A new sp_port is created every time we call serial_open (sp_get_port_by_name
implicitly creates one for us), so free it every time we call serial_close.
serial: Use new sp_set_config instead of sp_set_params.
Use new sp_port_config fields.
serial.c: Minor cosmetic fix.
ols: Always open serial port in nonblocking mode.

The scan() function was opening the port in non-blocking mode, the dev_open()
function however was not using the SERIAL_NONBLOCK flag. This led to hangs
in certain situations.

This fixes the OLS e.g. on NetBSD.
DT4000ZC/TP4000ZC: Force DTR=1 on the serial port.

This fixes the driver e.g. on NetBSD.
struitl: Add helper functions: string to number.
scpi: Add helper functions for scpi communication
scpi: Add function to strictly parse bool strings.
scpi: Add more functions (getting int/bool/float).
scpi: Add a function to read and wait on a *OPC? reply.
scpi: Add function to get an array of floats.
scpi: Add function to fetch uint8_t.