drm/amdgpu: HW setup of 2-level vmid0 page table

Set up HW for 2-level vmid0 page table: 1. Set up
PAGE_TABLE_START/END registers. Currently only plan
to do 2-level page table for ALDEBARAN, so only gfxhub1.0
and mmhub1.7 is changed. 2. Set page table base register.
For 2-level page table, the page table base should point
to PDB0. 3. Disable AGP and FB aperture as they are not
used.

Signed-off-by: Oak Zeng <Oak.Zeng@amd.com>
Reviewed-by: Christian Konig <christian.koenig@amd.com>
Reviewed-by: Felix Kuehling <felix.kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>