Introduce EN7581 SoC support with currently rfb board supported.
This is a new 64bit SoC from Airoha that is currently almost fully
supported upstream with only the DTS missing. Setting source-only
waiting for the full upstream support to be completed.
Link: https://github.com/openwrt/openwrt/pull/16730
Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>
