gpiolib: swnode: Remove wrong header inclusion

The flags in the software node properties are supposed to be
the GPIO lookup flags, which are provided by gpio/machine.h,
as the software nodes are the kernel internal thing and doesn't
need to rely to any of ABIs.

Fixes: e7f9ff5d

 ("gpiolib: add support for software nodes")
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>