drm/amdgpu: add vram reservation based on vram_usagebyfirmware_v2_2

Move TMR region from top of FB to 2MB for FFBM, so we need to
reserve TMR region firstly to make sure TMR can be allocated at 2MB

Signed-off-by: Tong Liu01 <Tong.Liu01@amd.com>
Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>