pinephone_defconfig: add support for early-boot status LED
This commit enables the green status LED (PD18/GPIO 114) on boot in the
SPL, in order to provide visual feedback that the PinePhone is booting.
Signed-off-by: Arnaud Ferraris <arnaud.ferraris@collabora.com> Reviewed-by: Andre Przywara <andre.przywara@arm.com> Reviewed-by: Samuel Holland <samuel@sholland.org> Tested-by: Samuel Holland <samuel@sholland.org> Signed-off-by: Andre Przywara <andre.przywara@arm.com>