drm-tests: swrast_test: check for EGL_KHR_no_config_context

eglCreateContext can only take a NULL config if the
EGL_KHR_no_config_context extension is supported by the driver. The
Mali and Imagination drivers don't support this, and passing in a
null config doesn't seem critical to the test, so let's add a check
here.

BUG=chromium:654131
TEST=swrast_test works on mali driver

Change-Id: I97fd1bf3477548f8bd746473636d09e5288b604e
Reviewed-on: https://chromium-review.googlesource.com/446013
Commit-Ready: Gurchetan Singh <gurchetansingh@chromium.org>
Tested-by: Gurchetan Singh <gurchetansingh@chromium.org>
Reviewed-by: Gurchetan Singh <gurchetansingh@chromium.org>
2 files changed