_mesa_meta_GenerateMipmap: Support all texture targets by generating shaders at runtime

_mesa_meta_GenerateMipmap: Support all texture targets by generating shaders at runtime

glsl path of _mesa_meta_GenerateMipmap() function would require different fragment
shaders depending on the texture target. This patch adds the code to generate
appropriate fragment shader programs at run time.
Fixes https://bugs.freedesktop.org/show_bug.cgi?id=54296

V2: Removed the code for integer textures as ARB is planning to
    disallow automatic mipmap generation for integer textures.
    Now using ralloc_asprintf in setup_glsl_generate_mipmap().

NOTE: This is a candidate for stable branches.

Signed-off-by: Anuj Phogat <anuj.phogat@gmail.com>
Reviewed-by: Brian Paul <brianp@vmware.com>