intel: Set screen's api mask according to hw capabilities (v3)

intel: Set screen's api mask according to hw capabilities (v3)

Before this patch, intelInitScreen2 set DRIScreen::api_mask with the hacky
heuristic below:

    if (gen >= 3)
        api_mask = GL | GLES1 | GLES2;
    else
        api_mask = 0;

This hack was likely broken on gen2 (i830), but I don't care enough to
properly investigate. It appears that every EGLConfig on i830 has
EGL_RENDERABLE_TYPE=0, and thus eglCreateContext will never succeed.
Anyway, moving on to living drivers...

With the arrival of EGL_OPENGL_ES3_BIT_KHR, this heuristic is now
insufficient. We must enable the GLES3 bit if and only if the driver is
capable of creating a GLES3 context. This requires us to determine the
maximum supported context version supported by the hardware/driver for
each api *during initialization of intel_screen*.

Therefore, this patch adds four new fields to intel_screen which indicate
the maximum supported context version for each api:
  max_gl_core_version
  max_gl_compat_version
  max_gl_es1_version
  max_gl_es2_version

The api mask is now correctly set as:

    api_mask = GL;
    if (max_gl_es1_version > 0)
        api_mask |= GLES1;
    if (max_gl_es2_version > 0)
        api_mask |= GLES2;

Tested against gen6 with piglit egl-create-context-verify-gl-flavor.
Verified that this patch does not change the set of exposed EGL context
flavors.

v2:
  - Replace the if-tree on gen with a switch, for Ian.
  - Unconditionally enable the DRI_API_OPENGL bit, for Ian.

v3:
  - Drop max gl version to 1.4 on gen3 if !has_occlusion_query,
    because occlusion queries entered core in 1.5. For Ian.

v4:
  - Drop ES2 version back to 2.0 due to rebase (Ian).

Signed-off-by: Chad Versace <chad.versace@linux.intel.com>
Reviewed-by: Ian Romanick <ian.d.romanick.intel.com>