drm/dp: Add Additional DP2 Headers

Include FEC, DSC, Link Training related headers.

Change since v2
- Align with the spec for DP_DSC_SUPPORT_AND_DSC_DECODER_COUNT

Signed-off-by: Fangzhi Zuo <Jerry.Zuo@amd.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Rodrigo Siqueira <rodrigosiqueiramelo@gmail.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210927192324.5428-1-Jerry.Zuo@amd.com