ARM: shmobile: Cleanup pm-rmobile.o build using Kconfig

Add a CONFIG_PM_RMOBILE entry and enable it for R-Mobile
SoCs in case CONFIG_PM is set. Consolidate Makefile power
management objects and get rid of #ifdefs in the C code.

Signed-off-by: Magnus Damm <damm+renesas@opensource.se>
Acked-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>