This adds the driver for I2C-based PCAL9535A GPIO chip.
This currently only enables minimal set of features of the chip for
very simple input/output operations, and does not support interrupt
yet.
Change-Id: I32ea07a71a38866280a96e68cff49cb0df12b85d
Signed-off-by: Daniel Leung <daniel.leung@intel.com>