EGL: translate EGL_GL_COLORSPACE_LINEAR_KHR to UNKNOWN

EGL_GL_COLORSPACE_KHR affects how GL blends and how the window
system interprets the pixel values.  Since LINEAR is the default, we
should treat it as we traditionally do

 - linear GL blending
 - UNKNOWN dataspace

The prior behavior is no longer possible until some new EGL extension
adds something like EGL_GL_COLORSPACE_SRGB_LINEAR.

Bug: 110389592
Test: boots and dumpsys to confirm
Change-Id: I1b7e8037ef042e9508f0efffb55602dfed27f937