Hibernate relies on cpu hotplug to prevent secondary cores executing
the kernel text while it is being restored.

Add a call to cpus_are_stuck_in_kernel() to determine if there are
CPUs not counted by 'num_online_cpus()', and prevent hibernate in this
case.

Fixes: 82869ac5 ("arm64: kernel: Add support for hibernate/suspend-to-disk")
Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: James Morse <james.morse@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>