drm/amdgpu: Move IB pool init and fini v2

Problem:
Using SDMA for TLB invalidation in certain ASICs exposed a problem
of IB pool not being ready while SDMA already up on Init and already
shutt down while SDMA still running on Fini. This caused
IB allocation failure. Temproary fix was commited into a
bringup branch but this is the generic fix.

Fix:
Init IB pool rigth after GMC is ready but before SDMA is ready.
Do th opposite for Fini.

v2: Remove restriction on SDMA early init and move amdgpu_ib_pool_fini

Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Andrey Grodzovsky <andrey.grodzovsky@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>