drm/amdgpu: Add gmc v12_0 ip block support (v7)

Add initial support for GMC v12.

v1: Add gmc v12_0 ip block support.
v2: Switch to gfx.kiq array.
v3: Switch to vmhubs_mask.
v4: Switch to AMDGPU_MMHUB0(0) and AMDGPU_GFXHUB(0)
v5: Rebase (Alex)
v6: Squash in fixes for AGP handling, gfxhub init order,
    vmhub index (Alex)
v7: Rebase (Alex)
v8: squash in ecc fix (Alex)

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>