drm/amdgpu/vce1: Check if VRAM address is lower than GART.

drm/amdgpu/vce1: Check if VRAM address is lower than GART.

Previously, I had assumed this was not possible
so it was OK to not handle it, but now we got a report
from a user who has a board that is configured this way.

When the VCPU BO is already located in a low 32-bit address
in VRAM (eg. when VRAM is mapped to the low address space),
don't do the workaround.

Fixes: 71aec08f80e7 ("amdgpu/vce: use amdgpu_gtt_mgr_alloc_entries")
Signed-off-by: Timur Kristóf <timur.kristof@gmail.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>