soc: renesas: Identify SoC and register with the SoC bus

soc: renesas: Identify SoC and register with the SoC bus

Identify the SoC type and revision, and register this information with
the SoC bus, so it is available under /sys/devices/soc0/, and can be
checked where needed using soc_device_match().

Identification is done using the Product Register or Common Chip Code
Register, as declared in DT (PRR only for now), or using a hardcoded
fallback if missing.

Example:

    Detected Renesas R-Car Gen2 r8a7791 ES1.0
    ...
    # cat /sys/devices/soc0/{machine,family,soc_id,revision}
    Koelsch
    R-Car Gen2
    r8a7791
    ES1.0

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