util: Add an aligned realloc function

util: Add an aligned realloc function

Mesa has one of these in imports.h, so u_memory needs one as well. This
is the version from mesa ported.

Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Reviewed-by: Kristian H. Kristensen <hoegsberg@google.com>
Reviewed-by: Matt Turner <mattst88@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/3024>