drm/amdgpu: add mmhub v3_0_2 ip callback functions

Unlike mmhub v3_0_0, there is no atc_l2 related
registers available in mmhub v3_0_2. Split the mmhub
v3_0_2 callback implementations from mmhub v3_0 so we
don't need to add ip version check when atc related
programming needs to be added to mmhub v3_0_0.

Signed-off-by: Hawking Zhang <Hawking.Zhang@amd.com>
Reviewed-by: Likun Gao <Likun.Gao@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>