ARM: smp: Use common outgoing-CPU-notification code

This commit removes the open-coded CPU-offline notification with new
common code. In particular, this change avoids calling scheduler code
using RCU from an offline CPU that RCU is ignoring. This is a minimal
change. A more intrusive change might invoke the cpu_check_up_prepare()
and cpu_set_state_online() functions at CPU-online time, which would
allow onlining throw an error if the CPU did not go offline properly.

Change-Id: I333b5ac50bb080134922727c1918182203af39ad
Signed-off-by: Maria Yu <aiquny@codeaurora.org>
Signed-off-by: Teng Fei Fan <tengfei@codeaurora.org>