utils/u_math: break dependency on gallium/utils

utils/u_math: break dependency on gallium/utils

Currently u_math needs gallium utils for cpu detection.  Most of what
u_math uses out of u_cpu_detection is duplicated in src/mesa/x86
(surprise!), so I've just reworked it as much as possible to use the
x86/common_x86_features.h macros instead of the gallium ones. The mesa
implementation is a header only approach, with no external dependencies.
There is one small function that was copied over, as promoting
u_cpu_detection is itself a fairly hefty undertaking, as it depends on
u_debug, and this fixes the bug for now.

bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=107870
Tested-by: Vinson Lee <vlee@freedesktop.org>