Do not imply that some of the generic headers may be always included.
Instead, include explicitly what we are direct user of.

While at it, drop unused linux/gpio.h and split out the GPIO group of
headers.
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>