drm/bridge: sii902x: Fix HDMI detection with DRM_BRIDGE_ATTACH_NO_CONNECTOR

drm/bridge: sii902x: Fix HDMI detection with DRM_BRIDGE_ATTACH_NO_CONNECTOR

The sii902x driver was caching HDMI detection state in a sink_is_hdmi field
and checking it in mode_set() to determine whether to set HDMI or DVI
output mode. This approach had two problems:

1. With DRM_BRIDGE_ATTACH_NO_CONNECTOR (used by modern display drivers like
TIDSS), the bridge's get_modes() is never called. Instead, the
drm_bridge_connector helper calls the bridge's edid_read() and updates the
connector itself. This meant sink_is_hdmi was never populated, causing the
driver to default to DVI mode and breaking HDMI audio.

2. The mode_set() callback doesn't receive atomic state or connector
pointer, making it impossible to check connector->display_info.is_hdmi
directly at that point.

Fix this by moving the HDMI vs DVI decision from mode_set() to
atomic_enable(), where we can access the connector via
drm_atomic_get_new_connector_for_encoder(). This works for both connector
models:

- With DRM_BRIDGE_ATTACH_NO_CONNECTOR: Returns the drm_bridge_connector
  created by the display driver, which has already been updated by the
helper's call to drm_edid_connector_update()

- Without DRM_BRIDGE_ATTACH_NO_CONNECTOR (legacy): Returns the connector
  embedded in sii902x struct, which gets updated by the bridge's own
get_modes()

Fixes: 3de47e1309c2 ("drm/bridge: sii902x: use display info is_hdmi")
Signed-off-by: Devarsh Thakkar <devarsht@ti.com>
Reviewed-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://patch.msgid.link/20251030151635.3019864-1-devarsht@ti.com