Pi3 and Compute Module 3 have a GPIO expander that the
VPU communicates with.
There is a mailbox service that now allows control of this
expander, so add a kernel driver that can make use of it.
Reviewed-by: NStefan Wahren <stefan.wahren@i2se.com>
Signed-off-by: NDave Stevenson <dave.stevenson@raspberrypi.org>
Signed-off-by: NBaruch Siach <baruch@tkos.co.il>
Signed-off-by: NLinus Walleij <linus.walleij@linaro.org>