Revert "cpufreq: dt: Add r8a7796 support to to use generic cpufreq driver"

This reverts commit bea2ebca.

This is no longer needed since the following commit and to the best
of my knowledge is not relied on by any upstream DTS:

edeec420 (cpufreq: dt-platdev: Automatically create cpufreq
device with OPP v2)

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>