!4339 修复pmem_legacy_device未被编译问题

Merge Pull Request from: @snoweay 
 
关联Issue https://gitee.com/openeuler/kernel/issues/I5BHF6

当前openeuler_defconfig 中CONFIG_LIBNVDIMM被设置为m时，drivers/nvdimm 目录不在obj-y中编译。
当CONFIG_PMEM_LEGACY=y时，需要将drivers/nvdimm/pmem_legacy_device.c 编译到kernel中,修改Makefile 
 
Link:https://gitee.com/openeuler/kernel/pulls/4339

 

Reviewed-by: zhangyi (F) <yi.zhang@huawei.com>
Signed-off-by: Jialin Zhang <zhangjialin11@huawei.com>