airoha: Add initial support for Airoha AN7581 SoC

Add initial support for Airoha AN7581 SoC. This adds the initial Kconfig
and Makefile entry for the SoC, an U-Boot specific DTSI and initial config
for it. Also add the initial code for CPU and RAM initialization.

Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>
14 files changed