Drivers which are not needed are built

For example, if I want i965 and radeonsi with opencl,
opencl => r600-llvm-compiler => video_cards_radeon
video_cards_radeon && classic => build r100 and r200
video_cards_radeon && !video_cards_r300 && !video_cards_r600 => build r300 and r600

This way all radeon drivers are built. What I propose is not to enable video cards automatically and only depend on r600-llvm-compiler when video_cards_r600 is enabled.

And an indentation fix.