MFC @ r259205 in preparation for some SVM updates. (for real this time)

Merge head up to r258343.

Adds gpioiic.4 and gpioled.4 man pages. Moves some of the information that
was previously available on gpio.4 to their respectives pages. Add the
cross references on gpioctl.8.

Approved by: adrian

Adds gpioiic.4 and gpioled.4 man pages. Moves some of the information that
was previously available on gpio.4 to their respectives pages. Add the
cross references on gpioctl.8.

Approved by: adrian (mentor)

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