In order to get ADV7180 analog video decoder to probe on a Gateworks
GW51xx we need select CONFIG_MUX_MMIO, otherwise /dev/media node does
not get created.

Select CONFIG_MUX_MMIO, so that the ADV7180 driver can be correctly
probed.
Reported-by: NTim Harvey <tharvey@gateworks.com>
Suggested-by: NSteve Longerbeam <slongerbeam@gmail.com>
Signed-off-by: NFabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: NShawn Guo <shawnguo@kernel.org>