[media] V4L: soc-camera: remove several now unused soc-camera client operations

This patch removes .enum_input(), .suspend() and .resume() soc-camera
client operations.

Functionality, provided by .enum_input(), if needed, can be implemented
using the v4l2-subdev API.

As for .suspend() and .resume(), the only client driver, implementing
these methods has been mt9m111, and the only host driver, using them
has been pxa-camera. Now that both those drivers have been converted
to the standard subdev .s_power() operation, .suspend() and .resume()
can be removed.

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>