drivers: gpio: gpio_mcux_igpio: add pull strength configuration

The i.MXRT10xx series have configurable GPIO pull strengths.

These are available for configuration in the pinctrl system, but not for
regular GPIO use.

This commit adds SOC-series specific GPIO configuration bits for selecting
weak or strong GPIO pulls, similar to drive strengths available from other
GPIO pin configuration examples.

This has been tested on a custom i.MXRT1062 product.

Signed-off-by: Stefan Giroux <stefan.g@feniex.com>