cpufreq: rcar: Add support for R8A7795 SoC

After the commit "a399dc9f

 cpufreq: shmobile: Use generic platdev
driver", will use cpufreq-dt-platdev driver to enable cpufreq-dt support.
Hence, follow the implementation to support new R8A7795 SoC.

Signed-off-by: Khiem Nguyen <khiem.nguyen.xt@rvc.renesas.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>