Adding a new platform: renesas rz

[Michele Bisogno]

Hi,

I've been a happy OpenWRT user for many years now, always buying
routers that could allow me to run it easily.

I've been working (actually only in my free time as a hobby) on
porting OpenWRT onto this Renesas board:
https://www.renesas.com/eu/en/products/microcontrollers-microprocessors/rz-mpus/rzg2l-evkit-rzg2l-evaluation-board-kit
which features this Arm Cortex-A55 based device:
https://www.renesas.com/eu/en/products/microcontrollers-microprocessors/rz-mpus/rzg2l-general-purpose-microprocessors-dual-core-arm-cortex-a55-12-ghz-cpus-and-single-core-arm-cortex-m33

I guess this is a new platform, since it does not really fit in any of
the already supported ones.

I got it working and I am polishing the patch before submitting it.
The support of this device is already mainlined in the Linux kernel,
so I am using 6.1 as is with the appropriate config.
Arm Trusted Firmware and u-boot are instead taken from the respective
Renesas forks, available on github.

However this is the first time I do that, and I am still reading and
learning, so I would like to get opinions, hints, why not constructive
criticism and hopefully encouragement.

For example, naming (renesas? renesas-rz? rz?) and structure of the
subfolders. There are other variants I would like to add: RZ/G2LC,
RZ/G2UL and maybe others.

System

HostnameOpenWrt
ModelRenesas SMARC EVK based on r9a07g044l2
ArchitectureARMv8 Processor rev 0
Target Platformrz/g2l
Firmware VersionOpenWrt SNAPSHOT r24187-bb8fd41f9a / LuCI Master
git-23.294.26440-30a8a0d
Kernel Version6.1.59
Local Time2023-10-29 07:44:17
Uptime0h 9m 11s
Load Average0.13, 0.08, 0.05