* Added test_mixer_routing_output_ctrl
* Added test_mixer_routing_input_ctrl
* Some minor mixer test and code improvements
* Update lib_xud dep version requirement
- Increases debug output when DEBUG flag set
- Removed some dead code
- Increased alignment of asm mixer functions
- Removed some usages of “xc_ptr” type in favour of native pointers in XC
- Added some asserts to mixer
- Added test_mixer_routing_input
- Moved test_mixer_routing_output to use shared code
- Various buffers no longer marked static to allow for easier unit testing
- Added some comments and removed some dead code from the implementation
- Moved mixer control comms to functions for unit test convenience