enabling the realtime clock 1-wire chip DS1307 and 1-wire on GPIO4 (as a module)

1-wire: Add support for configuring pin for w1-gpio kernel module
See: https://github.com/raspberrypi/linux/pull/457



Add bitbanging pullups, use them for w1-gpio

Allows parasite power to work, uses module option pullup=1

bcm2708: Ensure 1-wire pullup is disabled by default, and expose as module parameter

Signed-off-by: Alex J Lennon <ajlennon@dynamicdevices.co.uk>

w1-gpio: Add gpiopin module parameter and correctly free up gpio pull-up pin, if set

Signed-off-by: Alex J Lennon <ajlennon@dynamicdevices.co.uk>

w1-gpio: Sort out the pullup/parasitic power tangle