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>
diff --git a/arch/arm/Makefile b/arch/arm/Makefile
index 7334e79..5ecadb2 100644
--- a/arch/arm/Makefile
+++ b/arch/arm/Makefile
@@ -51,6 +51,7 @@
 
 # Machine directory name.  This list is sorted alphanumerically
 # by CONFIG_* macro name.
+machine-$(CONFIG_ARCH_AIROHA)		+= airoha
 machine-$(CONFIG_ARCH_APPLE)		+= apple
 machine-$(CONFIG_ARCH_ASPEED)		+= aspeed
 machine-$(CONFIG_ARCH_AT91)		+= at91