gpio: hlwd: Implement edge trigger emulation

Like the Spreadtrum EIC driver[1], this driver needs to emulate edge
triggered interrupts to support the generic gpio-keys driver.

[1]: https://www.spinics.net/lists/kernel/msg2764576.html



Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>