drm/vmwgfx: remove the default io_mem_pfn set

The default interface situation has been taken into the framework, so
remove the default set of each module.

Signed-off-by: Tan Xiaojun <tanxiaojun@huawei.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>