drm/ttm: de-inline ttm_bo_pin/unpin

Those functions are going to become more complex, don't inline them any
more.

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20220321132601.2161-4-christian.koenig@amd.com