gpio: gpiolib: Allow free() callback to be overridden

Allow free() callback to be overridden from irq_domain_ops for
hierarchical chips.

This allows drivers to free up resources which are allocated during
child_to_parent_hwirq()/populate_parent_alloc_arg() callbacks.

On Renesas RZ/G2L platform a bitmap is maintained for TINT slots, a slot
is allocated in child_to_parent_hwirq() callback which is freed up in free
callback hence this override.

Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Bartosz Golaszewski <brgl@bgdev.pl>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20220707182314.66610-5-prabhakar.mahadev-lad.rj@bp.renesas.com