i2c: img-scb: Drop METAG dependency

Now that arch/metag/ has been removed, remove the METAG dependency from
the IMG SCB I2C device driver. The hardware is also present on MIPS SoCs
so the driver still has value.

Signed-off-by: James Hogan <jhogan@kernel.org>
Acked-by: Wolfram Sang <wsa@the-dreams.de>
Cc: linux-i2c@vger.kernel.org
Cc: linux-metag@vger.kernel.org