mesa/glformats: Undo code changes from _mesa_base_tex_format() move

mesa/glformats: Undo code changes from _mesa_base_tex_format() move

The refactoring commit, c6bf1cd, accidentally reverted cd49b97
and 99b1f47. These changes caused more code to be added to the
function and removed the existing support for ASTC. This patch
reverts those modifications.

v2. Actually include ASTC support again.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=92221
Cc: "11.0" <mesa-stable@lists.freedesktop.org>
Signed-off-by: Nanley Chery <nanley.g.chery@intel.com>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>