media: dt-bindings: media: microchip,xisc: add bus-width of 14

The Microchip XISC supports a bus width of 14 bits.
Add it to the supported bus widths.

Signed-off-by: Eugen Hristev <eugen.hristev@microchip.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>