sw64: add basic NVDIMM support

Sunway inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I56OLG



--------------------------------

This patch introduces basic NVDIMM support for sw64:
  - Select ARCH_HAS_PMEM_API, ARCH_HAS_UACCESS_FLUSHCACHE and
    ARCH_HAS_ZONE_DEVICE in Kconfig.
  - Take bit 22 of pte as _PAGE_DEVMAP to support DAX.
  - Add some necessary functions for memory copy and cache flush.

Signed-off-by: Cui Mingrui <cuimingrui@wxiat.com>
Reviewed-by: He Sheng <hesheng@wxiat.com>
Signed-off-by: Gu Zitao <guzitao@wxiat.com>