media: img-ir: Drop METAG dependency

Now that arch/metag/ has been removed, remove the METAG dependency from
the IMG IR 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: Sean Young <sean@mess.org>
Cc: Mauro Carvalho Chehab <mchehab@s-opensource.com>
Cc: Mauro Carvalho Chehab <mchehab@kernel.org>
Cc: linux-media@vger.kernel.org
Cc: linux-metag@vger.kernel.org