msm_thermal: send OFF/ONLINE uevent in hotplug cases

Send the correct uevent after setting a CPU core online or offline.
This allows ueventd to set correct SELinux labels for newly created
sysfs CPU device nodes.

Bug: 28887345
Change-Id: If31b8529b31de9544914e27514aca571039abb60
Signed-off-by: Siqi Lin <siqilin@google.com>
Signed-off-by: Thierry Strudel <tstrudel@google.com>