C++ requires explicit casts from integers to enums. Fixes errors like
the following when trying to use Asahi GenXML from a GTest unit test.
src/asahi/lib/agx_pack.h:554:23: error: assigning to 'enum agx_channels' from incompatible type 'uint64_t' (aka 'unsigned long long')
values->channels = __gen_unpack_uint(cl, 0, 6);
Signed-off-by: Alyssa Rosenzweig <alyssa@rosenzweig.io>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/14903>