arm64/xen: implement ioremap_cached on arm64

Change-Id: I567349ba54959b45e817e8ebacbb8babca1ca453
Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Git-Repo: git://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/


Git-commit: 22d4102f778df9cab47e871b8de3400f6e685378
Signed-off-by: Abhimanyu Kapur <abhimany@codeaurora.org>