drm/ttm: add bo as parameter to the ttm_tt_create callback

Instead of calculating the size in bytes just to recalculate the number
of pages from it pass the BO directly to the function.

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Roger He <Hongbo.He@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>