drm/amdgpu: add VISIBLE info in amdgpu_bo_print_info

This allows tools to distinguish between VRAM and visible VRAM.

Use the opportunity to fix locking before accessing bo.

v2: squash in unused variable fix

Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>