Fix undefined symbols on non-x86 platforms

[riv19]

Fix error from issue #27 :

[alarm@localhost WebRip999]$ vspipe -c y4m tmp.vpy tets.y4m                                              
Warning: Failed to load /usr/lib/vapoursynth/libneo-f3kdb.so. Error given: /usr/lib/vapoursynth/libneo-f3kdb.so: undefined symbol: process_plane_impl_sse4_16bit_interleaved

No need for additional range checks, because at f3kdb.hpp:152 the code won't allow the array index to go beyond "C" optimization without detecting them on CPU.
UPD: but CPU capabilities return SSE support on ARM (it is hardcoded)... So that I had to fix it in another commit.

[riv19]

Unfortunately this SIMD optimization introduces artifacts on ARM. I had to set "opt=0" in Vapoursynth to disable.
But this is another topic - at least, it is possible to use the plugin on non-x86.
Ready for merge.