gpio: aggregator: Use compound literal from the header

Instead of doing it in place, convert GPIO_LOOKUP_IDX() and GPIO_HOG()
to be compund literals that's allow to use them as rvalue in assignments.

Due to above conversion, use compound literal from the header
in the gpio-aggregator.c.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>