i965: Call util_cpu_detect() early in screen creation

Fixes: a9618e7c ("util: Add accessor for util_cpu_caps")

This helps to avoid this assertion on i965 with debug builds:

• src/util/u_cpu_detect.h:116: util_get_cpu_caps: Assertion `util_cpu_caps.nr_cpus >= 1' failed.
• https://mesa-ci.01.org/mesa_master/builds/24807/results/3963618728 (gen9)
• https://mesa-ci.01.org/mesa_master/builds/24812/results/3969522980 (ivb)

I didn't reproduce this locally, but @robclark recommended this change, and it seems to help:

Adding this change, the https://mesa-ci.01.org/jljusten/builds/275/group/63a9f0ea7bb98050796b649e85481845

Cc: @kwg