r300g/swtcl: fix geometry corruption by uploading indices to a buffer

r300g/swtcl: fix geometry corruption by uploading indices to a buffer

The splitting of a draw call into several draw commands was broken, because
the split sometimes took place in the middle of a primitive. The splitting
was supposed to be dealing with the case when there are more indices than
the maximum size of a CS.

This commit throws that code away and uses a real index buffer instead.

https://bugs.freedesktop.org/show_bug.cgi?id=66558

Cc: mesa-stable@lists.freedesktop.org