Ensure that numeric array storage is aligned to 256-byte boundary.

OpenCL devices require this else we would get a performance hit.

(cherry picked from commit 03f7a342011a4f69cfcbec7af3e4f1a2e835618b)
(cherry picked from commit 757856e9275d19e2c7a3673d10fa8963fb9fbeb3)

Change-Id: Ie69e07dc5d9b62abad5cc39d1f30e1d770c56758
Reviewed-on: https://gerrit.libreoffice.org/8466
Reviewed-by: Michael Meeks <michael.meeks@collabora.com>
Tested-by: Michael Meeks <michael.meeks@collabora.com>