soc: aspeed: lpc: Add AST2600 compatible strings

The AST2600 has the same lpc-ctrl and lpc-snoop devices as the
AST2500.

Signed-off-by: Brad Bishop <bradleyb@fuzziesquirrel.com>
Acked-by: Andrew Jeffery <andrew@aj.id.au>
Link: https://lore.kernel.org/r/20190925125610.12096-4-bradleyb@fuzziesquirrel.com


Signed-off-by: Joel Stanley <joel@jms.id.au>