venus: vdec: a new function for output configuration

Make a new function vdec_output_conf() for decoder output
configuration. vdec_output_conf() will set properties via
HFI interface related to the output configuration, and
keep vdec_set_properties() which will set properties
related to decoding parameters.

Signed-off-by: Stanimir Varbanov <stanimir.varbanov@linaro.org>