arm64: Add "remove" probe driver for memory hot-remove

Allows to remove sections of memory that have been previously offlined
from userspace.

This is symmetric to the "memory probe" interface, as described in
Documentation/memory-hotplug.txt. It can be used to manually notify the
OS that one memory section has been removed.

Please, remind that a memory section can only be removed after it has
been logically off-lined; trying to remove a section which has not been
previously off-lined is not supported and will have undefined (but most
likely very bad) behaviour.

To offline a section one can:

To use the remove interface to remove the section:

where 0xYYYYYY is the physical address of the memory section to remove.

Change-Id: I1ab2fafe17b2697a5c667feae25c4ac0655f394e
Signed-off-by: Andrea Reale <ar@linux.vnet.ibm.com>
Signed-off-by: Maciej Bielski <m.bielski@virtualopensystems.com>
Patch-mainline: linux-kernel @ 11 Apr 2017, 18:25
Signed-off-by: Srivatsa Vaddagiri <vatsa@codeaurora.org>
Signed-off-by: Sudarshan Rajagopalan <sudaraja@codeaurora.org>