sun4i-cedar: Fix building as module

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
sunxi-hdmi: Fix NULL ptr deref when EDID info is received before fb is registered

With the latest changes hdmi_edid_received() calls lock_fb_info() now, but
calling lock_fb_info() on a not yet registered fb causes a NULL ptr exception.

This patch fixes this by tracking if the fb has been registered yet, and
only locking it if has (otherwise there will be no users of it, so no
locking will be necessary).

This patch also adds locking around the registered state trackig +
checking as hdmi_edid_received() gets called from the hdmi tasklet thread,
so it may race with Fb_Init().

Signed-off-by: Hans de Goede <hdegoede@redhat.com>