Clean up and rework FMOD.cmake and FindFMOD.cmake

FMOD.cmake:
	Move include(Prebuilt) to prebuilt section. It is only used for prebuilt anyway.
	set(FMOD_FIND_REQUIRED ON) due to FMOD variable is use elsewhere in cmake files. This behaviour is the same as openal.
	Remove redudent error messages and code due to above.
	Rework the logic to be more cleaner.
	Clean up whitespace.
FindFMOD.cmake
	Remove redudent paths as cmake allready uses them as default. Use PATH_SUFFIXES instead.
	The above will result in cmake looking in a lot more places and can handle custom build setups better.
	Change FMOD to FMOD_FOUND. FMOD should not be change withen cmake.
	Whitespace cleanup.