ARM: dts: aspeed: Add AST2600 and EVB

The AST2600 is a new SoC by ASPEED. It contains a dual core Cortex A7
CPU and shares many periperhals with the existing AST2400 and AST2500.

Link: https://lore.kernel.org/r/20190911165614.31641-1-joel@jms.id.au


Reviewed-by: Andrew Jeffery <andrew@aj.id.au>
Signed-off-by: Joel Stanley <joel@jms.id.au>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>