drm/amdgpu:fix amdgpu_sa_bo_new error(v2)

ib_pool init should prior to fbdev_init, otherwise
there will be error from amdgpu_sa_bo_new
(amdgpu_sa.c:323)

fbdev_init will call ttm_validate which further call
amdgpu_sa_bo_new.

v2:
move fbdev_init behind ib test.

Signed-off-by: Monk Liu <Monk.Liu@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>