ARM: dts: aspeed: ast2600evb: Enable i2c buses

With the exception of i2c10 and i2c11 which conflict with the pins
for the third and forth MDIO controllers.

i2c0 has an ADT7490 fan controller/thermal monitor device connected. The
devicetree describes an adt74490 on i2c0, however bus that it appears on
depends on jumper settings, so it may not be present on all EVBs. It is
included to assist testing of I2C.

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