radv: place pointer length into cache uuid

Thanks to reproducible builds, binary file timestamps may be identical
for both 32bit and 64bit packages when built from the same source.
This means radv will use the same cache for both 32 and 64 bit
processes, which leads to crashes.

Conveniently there is a spare byte in cache_uuid, let's place the
pointer size there.

Fixes: f4e499ec "radv: add initial non-conformant radv vulkan driver"
CC: 18.1 18.2 <mesa-stable@lists.freedesktop.org>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=107601
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=105904


Reviewed-by: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
(cherry picked from commit 356f6673)