Screen: Enable 10 bpc framebuffer support for AMD DCE-4 and later display engine.

Add neccessary setup code for DCE-4 ARGB2101010 framebuffer scanout enable,
and for "LUT bypass in 10 bpc mode". Same bits to twiddle, but different
registers on Evergreen and later.

Move crtcoff's array for DCE4+ head mapping from Linux screen glue into
PsychGraphicsCardRegisterSpecs.h to make it accessible anywhere in Screen.

Extend Screen/Linux and OSX PsychtoolboxKernelDriver to allow setting of
arbitrary user defined values for dither control register on AMD gpu's
via Screen('DisplayConfiguration', 'Dithering', screenId, headId, value);

Bonus: Screen('Null', screen, value); allows to query FMT_CLAMP_CONTROL on
AMD DCE-3 and later, and to set arbitrary value's as well. This as experiment
for some deep color tests. As usual, this is temporary.

Bonus: Some whitespace fixes in some files.

-> Screen.mex for 64-Bit Octave on Linux rebuilt.
-> Rebuild of Screen for other platforms and PsychtoolboxKernelDriver pending.