drm/amdgpu: put HQD EOP buffers into VRAM

This increases performance of compute queues.
EOP events (PKT3_RELEASE_MEM) are stored into these buffers.

Signed-off-by: Marek Olšák <marek.olsak@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>