i965: Use GL_RED for DEPTH_TEXTURE_MODE in ES 3.0 for unsized formats.

i965: Use GL_RED for DEPTH_TEXTURE_MODE in ES 3.0 for unsized formats.

Khronos has apparently decided that depth textures with sized formats
(allowed with ARB_internalformat_query or ES 3.0) should be treated as
GL_RED, while unsized formats (an existing feature) should be treated
as GL_INTENSITY for compatibility with ES 2.0.

Ian is proposing changes to ARB_internalformat_query which will make
this actually legal and consistent.

A similar problem exists with GL 4.2, but we're going to ignore that
for the time being.

Tested on Ivybridge: no Piglit regressions; fixes 4 es3conform tests:
- depth_texture_fbo
- depth_texture_fbo_clear
- depth_texture_teximage
- depth_texture_texsubimage

Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>