u_upload_mgr: pass alignment to u_upload_alloc manually

u_upload_mgr: pass alignment to u_upload_alloc manually

The fixed alignment of u_upload_mgr will go away.
This is the first step.

The motivation is that one u_upload_mgr can have multiple users,
each allocating from the same buffer, but requiring a different alignment.

Reviewed-by: Nicolai Hähnle <nicolai.haehnle@amd.com>