CPUFREQ: Loongson1: Rename the file to loongson1-cpufreq.c

CPUFREQ: Loongson1: Rename the file to loongson1-cpufreq.c

This patch renames the file to loongson1-cpufreq.c,
and also includes some minor updates.

Signed-off-by: Kelvin Cheung <keguang.zhang@gmail.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Cc: Rafael J. Wysocki <rjw@rjwysocki.net>
Cc: linux-pm@vger.kernel.org
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/13052/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>