arm64: cpu hotplug: ensure we mask out CPU_TASKS_FROZEN in notifiers

We have a couple of CPU hotplug notifiers for resetting the CPU debug
state to a sane value when a CPU comes online.

This patch ensures that we mask out CPU_TASKS_FROZEN so that we don't
miss any online events occuring due to suspend/resume.

Acked-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>