This adds support for configuring a gpio in udev to control the modem
power.
To enable gpio control, specify OFONO_QUECTEL_GPIO_CHIP and
OFONO_QUECTEL_GPIO_OFFSET in the udev environment, for example:
KERNEL=="ttymxc0", ENV{OFONO_DRIVER}="quectel", \
ENV{OFONO_QUECTEL_GPIO_CHIP}="gpiochip2", \
ENV{OFONO_QUECTEL_GPIO_OFFSET}="26"
Setup GSM 07.10 multiplexing using the kernel n_gsm line discpline
driver, and use the virtual tty devices as Aux and Modem channels.
The driver supports rts/cts on the underlying serial device. This is
enabled with OFONO_QUECTED_RTSCTS udev environment, e.g.:
KERNEL=="ttymxc0", ENV{OFONO_DRIVER}="quectel", \
ENV{OFONO_QUECTEL_RTSCTS}="on"