soc: renesas: rcar-sysc: Add DT support for SYSC PM domains
Populate the SYSC PM domains from DT, based on the presence of a device
node for the System Controller. The actual power area hiearchy, and
features of specific areas are obtained from tables in the C code.
The SYSCIER and SYSCIMR register values are derived from the power areas
present, which will help to get rid of the hardcoded values in R-Car H1
and R-Car Gen2 platform code later.
Initialization is done from an early_initcall(), to make sure the PM
Domains are initialized before secondary CPU bringup.