backends/drm: make icc profiles work with OpenGL ES

OpenGL doesn't support 1D textures, and has some special requirements in the shaders, like no implicit conversion from int to float

With "work" I really just mean that this one part of the pipeline works. Something else is broken with color management on GLES, everything's too dark and gray. But with this MR KWin at least doesn't crash because the driver doesn't support the OpenGL functions for 1D textures...