arm64, NUMA: Cleanup NUMA disabled messages

As noted by Dennis Chen, we don't want to print "No NUMA configuration
found" if NUMA was forced off from the command line.

Change the type of numa_off to bool, and clean up printing code.
Print "NUMA disabled" if forced off on command line and "No NUMA
configuration found" if there was no firmware NUMA information.

Signed-off-by: David Daney <david.daney@cavium.com>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Reviewed-by: Dennis Chen <dennis.chen@arm.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>