uce: pagecache reading scenario add shmem support

hulk inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I44R9D


CVE: NA

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

The call trace is as follows:
  __arch_copy_to_user+0x1bc/0x21c
  copy_page_to_iter+0xdc/0x328
  shmem_file_read_iter+0x124/0x350
  __vfs_read+0x11c/0x188
  vfs_read+0x94/0x150
  ksys_read+0x6c/0xd8
  __arm64_sys_read+0x24/0x30
  el0_svc_common+0x78/0x130
  el0_svc_handler+0x38/0x78
  el0_svc+0x8/0xc

This patch add uce kernel recovery path support in shmem_file_read_iter().

Signed-off-by: Tong Tiangen <tongtiangen@huawei.com>
Reviewed-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>