drm/amdgpu: change gartsize default to 256MB

Limit the default GART size and save a lot of VRAM.

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
4 files changed