drm/ttm: nuke ttm_bo_evict_mm and rename mgr function v3

Make it more clear what the resource manager function
does and nuke the wrapper function.

v2: nuke the wrapper
v3: fix typo in radeon, rebased

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch> (v2)
Link: https://patchwork.freedesktop.org/patch/393914/