drivers: sh: Disable PM runtime for multi-platform ARM with genpd

If the default PM Domain using PM_CLK is used for PM runtime, the real
Clock Domain cannot be registered from DT later.

Hence do not enable it when running a multi-platform kernel with genpd
support on R-Car or RZ.  The CPG/MSTP Clock Domain driver will take care
of PM runtime management of the module clocks.

Now most multi-platform ARM shmobile platforms (SH-Mobile, R-Mobile,
R-Car, RZ) use DT-based PM Domains to take care of PM runtime management
of the module clocks, simplify the platform logic by replacing the
explicit SoC checks by a single check for the presence of MSTP clocks in
DT.

Backwards-compatiblity with old DTs (mainly for R-Car Gen2) is provided
by checking for the presence of a "#power-domain-cells" property in DT.

The default PM Domain is still needed for:
  - backwards-compatibility with old DTs that lack PM Domain properties,
  - the CONFIG_PM=n case,
  - legacy (non-DT) ARM/shmobile platforms without genpd support
    (r8a7778, r8a7779),
  - legacy SuperH.

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>