gpio: mockup: drop unneeded includes

This module doesn't need gpio/consumer.h - it's a provider. It also
doesn't use any symbols from init.h so let's remove both includes.

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