drm/connector: hdmi: Fix kerneldoc warnings

It looks like the documentation for the HDMI-related fields recently
added to both the drm_connector and drm_connector_state structures
trigger some warnings because of their use of anonymous structures:

  $ scripts/kernel-doc -none include/drm/drm_connector.h
  include/drm/drm_connector.h:1138: warning: Excess struct member 'broadcast_rgb' description in 'drm_connector_state'
  include/drm/drm_connector.h:1138: warning: Excess struct member 'infoframes' description in 'drm_connector_state'
  include/drm/drm_connector.h:1138: warning: Excess struct member 'avi' description in 'drm_connector_state'
  include/drm/drm_connector.h:1138: warning: Excess struct member 'hdr_drm' description in 'drm_connector_state'
  include/drm/drm_connector.h:1138: warning: Excess struct member 'spd' description in 'drm_connector_state'
  include/drm/drm_connector.h:1138: warning: Excess struct member 'vendor' description in 'drm_connector_state'
  include/drm/drm_connector.h:1138: warning: Excess struct member 'is_limited_range' description in 'drm_connector_state'
  include/drm/drm_connector.h:1138: warning: Excess struct member 'output_bpc' description in 'drm_connector_state'
  include/drm/drm_connector.h:1138: warning: Excess struct member 'output_format' description in 'drm_connector_state'
  include/drm/drm_connector.h:1138: warning: Excess struct member 'tmds_char_rate' description in 'drm_connector_state'
  include/drm/drm_connector.h:2112: warning: Excess struct member 'vendor' description in 'drm_connector'
  include/drm/drm_connector.h:2112: warning: Excess struct member 'product' description in 'drm_connector'
  include/drm/drm_connector.h:2112: warning: Excess struct member 'supported_formats' description in 'drm_connector'
  include/drm/drm_connector.h:2112: warning: Excess struct member 'infoframes' description in 'drm_connector'
  include/drm/drm_connector.h:2112: warning: Excess struct member 'lock' description in 'drm_connector'
  include/drm/drm_connector.h:2112: warning: Excess struct member 'audio' description in 'drm_connector'

Create some intermediate structures instead of anonymous ones to silence
the warnings.

Reported-by: Jani Nikula <jani.nikula@linux.intel.com>
Suggested-by: Jani Nikula <jani.nikula@linux.intel.com>
Fixes: 54cb39e2 ("drm/connector: hdmi: Create an HDMI sub-state")
Fixes: 948f01d5 ("drm/connector: hdmi: Add support for output format")
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Signed-off-by: Maxime Ripard <mripard@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20240610111200.428224-1-mripard@kernel.org