drm/amdgpu: don't try to reserve training bo for sriov (v2)

1) SRIOV guest KMD doesn't care training buffer
2) if we resered training buffer that will overlap with IP discovery
reservation because training buffer is at vram_size - 0x8000 and
IP discovery is at ()vram_size - 0x10000 => vram_size -1)

v2: squash in warning fix from Nirmoy

Signed-off-by: Monk Liu <Monk.Liu@amd.com>
Reviewed-by: Emily Deng <Emily.Deng@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>