util: move check for AVX512
As a side effect solve:
[91/1401] Compiling C object src/util/libmesa_util.a.p/u_cpu_detect.c.o
../src/util/u_cpu_detect.c: In function '_util_cpu_detect_once':
../src/util/u_cpu_detect.c:889:11: warning: 'regs2[2]' may be used uninitialized [-Wmaybe-uninitialized]
889 | if (((regs2[2] >> 27) & 1) && // OSXSAVE
| ^~~~~~~~~~~~~~~~~~~~~~
../src/util/u_cpu_detect.c:823:16: note: 'regs2[2]' was declared here
823 | uint32_t regs2[4];
| ^~~~~
Edited by David Heidelberg