ACPI: docs: gpio-properties: Unify ASL style for GPIO examples

GPIO examples of ASL in the board.rst, enumeration.rst and gpio-properties.rst
are not unified. Unify them for better reader experience.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>