MIPS: Don't register r4k sched clock when CPUFREQ enabled

MIPS: Don't register r4k sched clock when CPUFREQ enabled

Don't register r4k sched clock when CPUFREQ enabled because sched clock
need a constant frequency.

Signed-off-by: Huacai Chen <chenhc@lemote.com>
Cc: John Crispin <john@phrozen.org>
Cc: Steven J . Hill <Steven.Hill@caviumnetworks.com>
Cc: Fuxin Zhang <zhangfx@lemote.com>
Cc: Zhangjin Wu <wuzhangjin@gmail.com>
Cc: linux-mips@linux-mips.org
Cc: stable@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/13820/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>