drm/amdgpu: Fix offset for HDP remap in nbio v7.11

APUs in passthrough mode use HDP flush. 0x7F000 offset used for
remapping HDP flush is mapped to VPE space which could get power gated.
Use another unused offset in BIF space.

Signed-off-by: Lijo Lazar <lijo.lazar@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit d8116a32)
Cc: stable@vger.kernel.org