x86: pmem: move persistent memory(legacy) code into nvdimm

hulk inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I4O31I



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Move x86's pmem.c into nvdimm, and rename X86_PMEM_LEGACY_DEVICE to
PMEM_LEGACY_DEVICE, also add PMEM_LEGACY to control the built of
nd_e820.o, then the code could be reused by other architectures.

Note，this patch fixs the nd_e820.c build introduced by commit 2499317e
("arm64: Revert feature: Add memmap parameter and register pmem").

Signed-off-by: Zhuling <zhuling8@huawei.com>
Reviewed-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>