util: Add cpuinfo-i386.c

util: Add cpuinfo-i386.c

Add cpuinfo.h for i386 and x86_64, and the initialization
for that in util/.  Populate that with a slightly altered
copy of the tcg host probing code.  Other uses of cpuid.h
will be adjusted one patch at a time.

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>