drm/amd/display: Add DP 2.0 HPO Stream Encoder

HW Blocks:

        +--------+  +-----+  +------+
        |  OPTC  |  | HDA |  | HUBP |
        +--------+  +-----+  +------+
            |          |        |
            |          |        |
    HPO ====|==========|========|====
     |      |          v        |
     |      |       +-----+     |
     |      |       | APG |     |
     |      |       +-----+     |
     |      |          |        |
     v      v          v        v
           +----------------------+
           |  HPO Stream Encoder  |
           +----------------------+

[squash in warning fixes - Alex]

Signed-off-by: Fangzhi Zuo <Jerry.Zuo@amd.com>
Reviewed-by: Nicholas Kazlauskas <Nicholas.Kazlauskas@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>