drivers: gpio_nrfx: support edge interrupts using GPIO SENSE

Currently level interrupts are implemented using GPIO SENSE, but edge
interrupts using GPIOTE events. Using GPIOTE events results in increased
power consumption according to product specifications and erratas of
some nRF MCUs. In case of nRF52832 it is <20uA in System ON Idle and
~400-450uA when used in conjunction with SPI or TWI.

Add a user configurable option to select between GPIOTE events and GPIO
SENSE mechanism, for implementing edge interrupts. Selecting GPIO SENSE
option will allow to reduce power consumption in scenarios mentioned by
nRF MCUs erratas.

Additionally GPIO SENSE mechanism (as opposed to GPIOTE event) allows to
detect state changes of pins configured as output.

Signed-off-by: Marcin Niestroj <m.niestroj@grinn-global.com>