Implement pads control for GPIO pins

[lategoodbye]

According to GPIO pads control document the BCM2835 GPIOs also support the following settings:

• output slew rate
• input hysteresis
• output drive strength

So this should be implemented in the GPIO driver. Maybe we need to convert it into a standard GPIO driver before.

[lategoodbye]

For pads control we need to take of the following points:

• registers are located within power management
• control applies to banks not pins

So i would start with a separate driver.