Introduce generic bitbang I2C system, and a s3c24xx-specific implementation of
it that knows which GPIO pins and how to control them.
The generic bitbang stuff exposes synchronous (ie, it will return when it is
done) and asynchronous read and write APIs, allowing the delay between bits to
be hidden in other slow, looping code if necessary.
Signed-off-by: Andy Green <andy@openmoko.com>
