gallium/util: add alignment parameter to util_upload_index_buffer

At least on Mali Utgard, index buffers need to be aligned on 0x40.
To avoid duplicating this, add an alignment parameter.
Keep the previous default for the other existing users.

Signed-off-by: Erico Nunes <nunes.erico@gmail.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/2445>
6 files changed