arm64: allwinner: a64: allow laptops to wake up from lid

Currently all ARM kernels will have s2idle enabled if CONFIG_SUSPEND is
present. In this case if the lid is closed, systemd-logind will enter
s2idle mode by default; however there's no possible wakeup source
defined, so the system will enter a forever idle.

Add the lid itself as a wakeup source, thus the system can wakeup when
the lid is opened.

Signed-off-by: Icenowy Zheng <icenowy@aosc.io>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>