gallium/hud: add CPU usage support for FreeBSD

Reviewed-by: Eric Engestrom <eric@engestrom.ch>
15 jobs for !372 with hud-cpu-fbsd in 16 minutes and 16 seconds (queued for 2 seconds)
detached
Status Job ID Name Coverage
  Containers Build
passed #219543
ubuntu

00:00:17

 
  Build+Test
passed #219544
autotools

00:15:57

passed #219546
meson-clang

00:13:06

passed #219552
meson-gallium-clover-llvm

00:06:33

passed #219553
meson-gallium-clover-llvm39

00:04:53

passed #219551
meson-gallium-drivers-other

00:06:31

passed #219550
meson-gallium-radeonsi

00:05:56

passed #219554
meson-gallium-st-other

00:06:28

passed #219545
meson-gallium-swr

00:13:00

passed #219549
meson-glvnd

00:07:14

passed #219548
meson-loader-classic-dri

00:08:45

passed #219547
meson-vulkan

00:04:30

passed #219556
scons-llvm

00:06:16

passed #219555
scons-nollvm

00:05:50

passed #219557
scons-swr

00:05:52