PCA957x is i2c gpio expander, and similar to PCA953x. Although register
configurations are different between PCA957x and PCA953x. They can share
a lot of components, such as IRQ handling, GPIO IN/OUT. So updating PCA953x
driver to support PCA957x chips.
Signed-off-by: Haojian Zhuang <haojian.zhuang@marvell.com>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>