msm: hotplug: Block hotplug removal of CPU0

Hotplug removal of CPU0 is not currently supported. Attempts to
remove it may result in undefined behaviour. Explicitly block
any such attempts before other hotplug notifiers get the chance
to run by setting the notifier priority to INT_MAX.

Change-Id: I9e1f5b4a0db554295a097220417f2bdf4c690f5f
Signed-off-by: Matt Wagantall <mattw@codeaurora.org>