sunxi: GPIO pin mux hardware-feature-specific function index defines

Each hardware feature exposed through the GPIO pin mux is usually using the same
function index (for a given port), so there is no need to define one value per
pin: one value per hardware feature per port is sufficient, avoids duplication
and makes everything easier to understand.

Signed-off-by: Paul Kocialkowski <contact@paulk.fr>
Acked-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>