Several API changes from 4.18 to 5.0

Trivial

ib_device_ops

function int ib_fmr_pool_unmap() -> void ib_fmr_pool_unmap()

DECLARE_PCI_UNMAP_ADDR() dropped

4.16: kernel_sock_ioctl() helper function dropped

Fix up inode_has_no_xattr() now that MS_* and SB_* flags have split.

4.18: kernel inode i_mtime, i_atime, i_ctime are timespec64

4.19: kernel ext4_iget() now takes a flags argument

4.20: iov_iter_type is defined breaking a macro only used by lustre

Provide accessor wrapper for:

kernel 5.0 commit ca79b0c211af63fa3276f0e3fd7dd9ada2439839
mm: convert totalram_pages and totalhigh_pages variables to atomic

 kernel 4.19 vfs 'atomic_open' changed signature. Use FMODE_CREATED flag instead of '*opened' argument.

kernel 5.1 commit 3d252529480c68bfd6a6774652df7c8968b28e41
SELinux: Remove unused selinux_is_enabled

(commit 3d252529480 included in ubuntu 5.0 kernel)

Provide .m4 macros and wrappers as needed.

(Mostly trivial changes on top of changes for RHEL8).