Remove usage WITH_CYCLES_CUDA_BINARIES in code, use check for

precompiled cubins instead,

Logic here is following now:
- If there're precompiled cubins, assume CUDA compute is available,
  otherwise
- If cuda toolkit found, assume CUDA compute is available
- In all other cases CUDA compute is not available

For windows there're still check for only precompiled binaries,
no runtime compilation is allowed.

Ended up with such decision after discussion with Brecht. The thing
is, if we'll support runtime compilation on windows we'll end up
having lots of reports about different aspects of something doesn't
work (you need particular toolkit version, msvc installed, environment
variables set properly and so) and giving feedback on such reports
will waste time.

intern/cycles/CMakeLists.txt

@@ -47,10 +47,6 @@ if(WITH_CYCLES_OSL)
 	include_directories(${OSL_INCLUDES})
 endif()
 
-if(WITH_CYCLES_CUDA_BINARIES)
-	add_definitions(-DWITH_CUDA_BINARIES)
-endif()
-
 add_definitions(-DWITH_OPENCL)
 add_definitions(-DWITH_CUDA)
 add_definitions(-DWITH_MULTI)