drm/i915/bios: reserve struct bdb_ prefix for BDB blocks

Don't use bdb_ prefixes for structs within blocks. Add a new bdb struct
for SDVO panel DTDs for completeness.

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/cd062ced1bbbe07e087212b42c83e5ac64a22a49.1559308269.git.jani.nikula@intel.com