nvk: Rework side-band data upload

nvk: Rework side-band data upload

Instead of doing magic alignments, it now takes an explicit alignment
parameter.  Also, we now have a version of the helper which does the
memcpy.  This should encourage users to avoid reading reading upload
maps in case they're ever write-combine in the future.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/24326>