soc: renesas: Move power-domain drivers to the genpd dir

To simplify with maintenance let's move the renesas power-domain drivers to
the new genpd directory. Going forward, patches are intended to be managed
through a separate git tree, according to MAINTAINERS.

Cc: Geert Uytterhoeven <geert+renesas@glider.be>
Cc: Magnus Damm <magnus.damm@gmail.com>
Cc: <linux-renesas-soc@vger.kernel.org>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>