drm/bridge: dw-hdmi: handle ELD when DRM_BRIDGE_ATTACH_NO_CONNECTOR

The current ELD handling takes the internal connector ELD buffer and
shares it to the I2S and AHB sub-driver.

But with DRM_BRIDGE_ATTACH_NO_CONNECTOR, the connector is created
elsewhere (or not), and an eventual connector is known only
if the bridge chain up to a connector is enabled.

The current dw-hdmi code gets the current connector from
atomic_enable() so use the already stored connector pointer and
replace the buffer pointer with a callback returning the current
connector ELD buffer.

Since a connector is not always available, either pass an empty
ELD to the alsa HDMI driver or don't call snd_pcm_hw_constraint_eld()
in AHB driver.

Reported-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
[narmstrong: fixed typo in commit log]
Acked-by: Jernej Skrabec <jernej.skrabec@gmail.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211029135947.3022875-1-narmstrong@baylibre.com