ARM: shmobile: R-Mobile: Use generic_pm_domain.attach_dev() for pm_clk setup

Use the just introduced genpd attach/detach callbacks to register the
devices' module clocks, instead of doing it directly, to make it
DT-proof.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>