Clean spatial picture alloc code
remove duplicate function
Remove stub interfaces for hw decoding

There is no implementation available for actually doing decoding
in HW.
Merge pull request #285 from volvet/develop_b

remove duplicated function
Merge pull request #284 from volvet/clean_spatial_picture_code

Clean spatial picture alloc code
use forward declaration to replace type cast
Merge pull request #288 from volvet/develop_b

use forward declaration to replace type cast
Merge pull request #286 from mstorsjo/remove-hw-decode

Remove stub interfaces for hw decoding