video_core: Silent miscellaneous warnings (#2820)

* texture_cache/surface_params: Remove unused local variable

* rasterizer_interface: Add missing documentation commentary

* maxwell_dma: Remove unused rasterizer reference

* video_core/gpu: Sort member declaration order to silent -Wreorder warning

* fermi_2d: Remove unused MemoryManager reference

* video_core: Silent unused variable warnings

* buffer_cache: Silent -Wreorder warnings

* kepler_memory: Remove unused MemoryManager reference

* gl_texture_cache: Add missing override

* buffer_cache: Add missing include

* shader/decode: Remove unused variables