OMAPDSS: VENC: allow switching venc type at runtime

OMAPDSS: VENC: allow switching venc type at runtime

VENC type (composite/svideo) doesn't have to be fixed by board wiring,
it is possible to provide both connectors, which is what pandora does.
Having to recompile the kernel for users who have TV connector types
that's don't match default board setting is very inconvenient, especially
for users of a consumer device, so add support for switching VENC type
at runtime over a new sysfs file venc_type.

Signed-off-by: Grazvydas Ignotas <notasas@gmail.com>