egl/dri2: expose srgb configs when KHR_gl_colorspace is available

egl/dri2: expose srgb configs when KHR_gl_colorspace is available

Otherwise the user has no way of using it, and we'll try to access the
linear one.

v2:
 - Bail out when KHR_gl_colorspace is missing and srgb is set (Marek)

Cc: Chih-Wei Huang <cwhuang@android-x86.org>
Cc: "11.0 11.1" <mesa-stable@lists.freedesktop.org>
Fixes: c2c2e9ab604(egl: implement EGL_KHR_gl_colorspace (v2))
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=91596
Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>
Tested-by: Mauro Rossi <issor.oruam@gmail.com>