Merge branch 'bugfix/workaround_gpio_pullupdown_bug' into 'master'

Work around the GPIO pullup/pulldown SoC bug

Some GPIO pins need to have their pullups/pulldowns set in the RTC peripheral instead of in the GPIO peripheral because of a silicon bug.

This merge:
- Declares PIN_PULLUP_EN and friends as deprecated; they can't really be changed to work around the issue because they get passed an iomux register instead of an io pin number
- Adds gpio_pullup_en and friends to the GPIO driver. These functions do have the workaround (as well as all the other functions in the gpio driver) and are meant to easily replace the PIN_PULLUP_EN routines
- Fixes some comments in the gpio headers

See merge request !200