arm64: default NR_CPUS to 256

There are shipping arm64 platforms with 256 hardware threads. So that we
can make use of these with defconfig, bump the arm64 default NR_CPUS to
256.

At the same time, drop a redundant comment. We only have one default for
NR_CPUS, so there's nothing to sort.
Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/Kconfig

@@ -792,8 +792,7 @@ config SCHED_SMT
 config NR_CPUS
 	int "Maximum number of CPUs (2-4096)"
 	range 2 4096
-	# These have to remain sorted largest to smallest
-	default "64"
+	default "256"
 
 config HOTPLUG_CPU
 	bool "Support for hot-pluggable CPUs"