Use the static TexStorage2|3D funcs in es builds

When building with -opengl es2 and having ES 3.0 or newer, TexStorage must resolve
directly to the functions.

Other paths (desktop, ES when using dynamic on Windows) are already covered below.

Change-Id: If214578bf23547d6f66a17bc999e9fabf97ba770
Reviewed-by: Giuseppe D'Angelo <giuseppe.dangelo@kdab.com>