drm/amdgpu: add debugfs for kfd system and ttm mem used

This keeps track of kfd system mem used and kfd ttm mem used.

Signed-off-by: Alex Sierra <alex.sierra@amd.com>
Reviewed-by: Philip Yang <Philip.Yang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>