clk: shmobile: Add CPG/MSTP Clock Domain support

Add Clock Domain support to the Clock Pulse Generator (CPG) Module Stop
(MSTP) Clocks driver using the generic PM Domain.  This allows to
power-manage the module clocks of SoC devices that are part of the
CPG/MSTP Clock Domain using Runtime PM, or for system suspend/resume.

SoC devices that are part of the CPG/MSTP Clock Domain and can be
power-managed through an MSTP clock should be tagged in DT with a
proper "power-domains" property.

The CPG/MSTP Clock Domain code will scan such devices for clocks that
are suitable for power-managing the device, by looking for a clock that
is compatible with "renesas,cpg-mstp-clocks".

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Stephen Boyd <sboyd@codeaurora.org>
Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org>
Reviewed-by: Kevin Hilman <khilman@linaro.org>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>