drm/amdgpu: fix 4-level paging if GMC supports 57-bit VA v2

drm/amdgpu: fix 4-level paging if GMC supports 57-bit VA v2

It turned that using 4 level page tables on GMC generations which support
57bit VAs actually doesn't work at all.

Background is that the GMC actually can't switch between 4 and 5 levels,
but rather just uses a subset of address space when less than 5 levels are
selected.

Philip already removed the automatically switch to 4levels, now fix it as
well should it be enabled by module parameters.

v2: fix AMDGPU_GMC_HOLE_MASK as well, fix off by one issue pointed out
    by Philip

Signed-off-by: Christian König <christian.koenig@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Philip Yang <philip.yang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>