egl/android: Provide an option for the backend to expose KHR_image

egl/android: Provide an option for the backend to expose KHR_image

From android cts 8.0_r4, a new test case checks if all the required egl
extensions are exposed. In the current implementation we expose KHR_image
if KHR_image_base and KHR_image_pixmap are supported but KHR_image spec
does not mandate the existence of both the extensions.
This patch preserves the current check and also provides the backend
with an option to expose the KHR_image extension.

Test: run cts -m CtsOpenGLTestCases -t \
android.opengl.cts.OpenGlEsVersionTest#testRequiredEglExtensions

Signed-off-by: Harish Krupo <harish.krupo.kps@intel.com>
Reviewed-by: Tapani Pälli <tapani.palli@intel.com>
Reviewed-by: Eric Engestrom <eric.engestrom@imgtec.com>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>