drivers: ublox-sara-r4: Add support for pin polarity

[sslupsky]

The current ublox sara r4 driver assumes polarity of the POWER, RESET and VINT pins. Presently, the Arduino MKR NB 1500 inverts the polarity of the POWER and RESET pins (it does not have a VINT pin). This is a result of a level translator (N-channel FET) between the mcu pin and the SARA-R4 pin.

Describe the solution you'd like
To support the Arduino board, it is necessary to implement a polarity inversion function. The SAMD21 soc does not support hardware pin inversion so setting the gpio flags will not address this problem.

Suggested changes:

modem_context.h:
Add a polarity member to struct modem_pin.
Add polarity to MODEM_PIN macro

modem_pin.c:
Add polarity to modem_pin_read(), modem_pin_write(), modem_pin_config() and modem_pin_init().

ublox-sara-r4.c:
Add polarity to initialization of modem_pins[]

ublox,sara-r4.yaml:
Add polarity settings mdm-power-pol, mdm-reset-pol, mdm-vint-pol

I can create a PR for this but before I do I would like to seek some feedback on my proposed change to the modem drivers and the SARA R4 driver.

[sslupsky]

The new GPIO API fixes this issue. Though, for some reason, the driver reverted to using the "raw" pin. My PR sets this back to using gpio_pin_set() which will enable logical pin setting (Active High or Active Low).
#24042