drivers: clock_control: add R-Car CPG MSSR driver

Clock Pulse Generator, Module Standby Software Reset, are registers
presents in Renesas Gen3 SoC series.

MSSR is used to supply clock to the different modules, shuch as timer,
or UART, it's also possible to issue a reset the different module.

CPG registers allow to get the rate or to set some divider like for
the CAN clock.

Signed-off-by: Julien Massot <julien.massot@iot.bzh>
diff --git a/CODEOWNERS b/CODEOWNERS
index f73ffc2..2d53bb2 100644
--- a/CODEOWNERS
+++ b/CODEOWNERS
@@ -184,6 +184,7 @@
 /drivers/can/*mcp2515*                    @karstenkoenig
 /drivers/clock_control/*nrf*              @nordic-krch
 /drivers/clock_control/*esp32*            @extremegtx
+/drivers/clock_control/*rcar*             @julien-massot
 /drivers/counter/                         @nordic-krch
 /drivers/console/ipm_console.c            @finikorg
 /drivers/console/semihost_console.c       @luozhongyao