arm: highmem: Fix CPU_DYING callback for kmap

Add CPUHP_AP_KMAP_DYING state support instead of
use cpu notify for CPU_DYING which is deprecated.

Change-Id: Idaaf628ef4c89f361391151db523f5ffefc5bcc1
Signed-off-by: Maria Yu <aiquny@codeaurora.org>
Signed-off-by: Kaushal Kumar <kaushalk@codeaurora.org>