drm/amdgpu: psp DTM init

DTM is the display topology manager. This is needed to communicate with
psp about the display configurations.

This patch adds
    -Loading the firmware
    -The functions and definitions for communication with the firmware

v2: Fix formatting

Signed-off-by: Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>