ARM: shmobile: R-Mobile: Move pm-rmobile to drivers/soc/renesas/

The pm-rmobile driver is really a driver for the System Controller
(SYSC) found in R-Mobile SoCs.  An equivalent driver for R-Car SoCs is
already located under drivers/soc/renesas/.

Hence move the pm-rmobile driver from arch/arm/mach-shmobile/ to
drivers/soc/renesas/, and rename it to rmobile-sysc.

Enable compile-testing on non-ARM and non-R-Mobile SoCs.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>