drm/amdgpu: Remove VRAM from shared bo domains.

This fixes an issue introduced by change "allow framebuffer in GART
memory as well" which could lead to a shared buffer ending up
pinned in vram.  Use GTT if it is included in the domain, otherwise
return an error.

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