ARM: dts: aspeed: tacoma: Enable eMMC controller

Enabling emmc without enabling its controller doesn't do any good.
Enable its controller as well to make it work.

Cc: Andrew Jeffery <andrew@aj.id.au>
Cc: Joel Stanley <joel@jms.id.au>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Joel Stanley <joel@jms.id.au>