arm64: Honor limits set by boot parameter

Consider the memory limit enforced by boot parameter and
restrict adding beyond this boundary during a memory hotplug.

Change-Id: Ibd13e47ee13004381a1ddff649150fae13429c87
Signed-off-by: Vijayanand Jitta <vjitta@codeaurora.org>
Signed-off-by: Isaac J. Manjarres <isaacm@codeaurora.org>