cpufreq: mediatek: Add support of cpufreq to MT2701/MT7623 SoC

MT2701/MT7623 is a 32-bit ARMv7 based quad-core (4 * Cortex-A7) with
single cluster and this hardware is also compatible with the existing
driver through enabling CPU frequency feature with operating-points-v2
bindings. Also, this driver actually supports all MediaTek SoCs, the
Kconfig menu entry and file name itself should be updated with more
generic name to drop "MT8173"

Signed-off-by: Sean Wang <sean.wang@mediatek.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Reviewed-by: Jean Delvare <jdelvare@suse.de>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>