xen/arm and xen/arm64: implement HYPERVISOR_tmem_op

Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Git-commit: 176455e9a9e2a37a0b3eec6f6d7883de720c02c7
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


Signed-off-by: Ian Maund <imaund@codeaurora.org>