nvidia_gpus: style beautifier
opencl: do not use NVIDIA sm20 extensions with Mac OpenCL

the OSX opencl compiler does not understand inline asm instructions.
therefore we need to treat all NVIDIA GPUs on Macs as if they have no
atomic_add_f32 and use emulation code instead.
(cherry picked from commit 957f2225aa6859fc2d73eeb706ea5f1f7c56cdc2)
opencl: fix for #9547
(cherry picked from commit 8ebc2a15d14a5b92613c070a52e40d04a8d7ebce)
exposure: disable autoexposure when switching images
(cherry picked from commit 5135386384e6fd0c0c621e8aa82e4b375e8905a7)
(cherry picked from commit e6a531acd4b6ebe133ce97f598c695b536758215)