TI PCA9536 is 4-Bit I2C GPIO expander without interrupt support[1].
Add support for the same.

[1] TRM: http://www.ti.com/lit/ds/symlink/pca9536.pdfSigned-off-by: Vignesh R <vigneshr@ti.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>