arm: rmobile: Add CPU detection for RZ/G2L

arm: rmobile: Add CPU detection for RZ/G2L

The ARM TrustedFirmware code for the Renesas RZ/G2L SoC family passes a
devicetree blob to the bootloader as an argument in the same was
previous R-Car Gen3/Gen4 SoCs. This blob contains a compatible string
which can be used to identify the particular SoC we are running on.

We do this as reading the DEVID & PRR registers from u-boot is not
sufficient to differentiate between the R9A07G044L (RZ/G2L) and
R9A07G044C (RZ/G2LC) SoCs. An additional read from offset 0x11861178 is
needed but this address is in the OTP region which can only be read from
the secure world (i.e. TrustedFirmware). So we have to rely on
TrustedFirmware to determine the SoC and pass this information to u-boot
via an fdt blob.

Signed-off-by: Paul Barker <paul.barker.ct@bp.renesas.com>
Reviewed-by: Biju Das <biju.das.jz@bp.renesas.com>
Reviewed-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Reviewed-by: Marek Vasut <marek.vasut+renesas@mailbox.org>