tools: gpio: implement gpio-watch

Add a simple program that allows to test the new LINECHANGED_FD ioctl().

Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>

tools: gpio: Correctly add make dependencies for gpio_utils

gpio tools fail to build correctly with make parallelization:

$ make -s -j24
ld: gpio-utils.o: file not recognized: file truncated
make[1]: *** [/home/labbott/linux_upstream/tools/build/Makefile.build:145: lsgpio-in.o] Error 1
make: *** [Makefile:43: lsgpio-in.o] Error 2
make: *** Waiting for unfinished jobs....

This is because gpio-utils.o is used across multiple targets.
Fix this by making gpio-utios.o a proper dependency.

Cc: <stable@vger.kernel.org>
Signed-off-by: Laura Abbott <labbott@redhat.com>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>

tools/gpio: move to tools buildsystem

There is a nice buildsystem dedicated for userspace tools in Linux kernel tree.
Switch gpio target to be built by it.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Alexandre Courbot <acourbot@nvidia.com>
Tested-by: Alexandre Courbot <acourbot@nvidia.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>