i965/gen4: Pull texture formats from the texture object not the miptree

i965/gen4: Pull texture formats from the texture object not the miptree

This makes texture views sort-of work.  It doesn't add full texture view
support for gen4-5 but it is enough to fix the GL_ARB_copy_image formats
piglit test on Iron Lake.

Signed-off-by: Jason Ekstrand <jason@jlekstrand.net>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=83036
Cc: "11.1 11.2 12.0" <mesa-stable@lists.freedesktop.org>
(cherry picked from commit ee39d3ba918de9d52d79bdee6db2c120bcf0f28e)