Add extended sRGB linear known transfer function
Based upon the wording in https://registry.khronos.org/EGL/extensions/EXT/EGL_EXT_gl_colorspace_scrgb_linear.txt
This can be achieved already by using linear + set luminances, however not all compositors will implement that, but probably want to support this TF as it is very commonly used in games and desktop applications.
Signed-off-by: Joshua Ashton joshua@froggi.es