No one will use this function except ttm_bo_io_mem_pfn() now, so move
the calculation of ttm_bo_default_io_mem_pfn() into ttm_bo_io_mem_pfn()
and do some cleanup.
Signed-off-by: NTan Xiaojun <tanxiaojun@huawei.com>
Reviewed-by: NChristian König <christian.koenig@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>