cpufreq: ondemand: Update the efficient idle check for Intel extended Families

cpufreq: ondemand: Update the efficient idle check for Intel extended Families

IO time is considered busy by default for modern Intel processors. The
current check covers recent Family 6 models but excludes the brand new
Families 18 and 19.

According to Arjan van de Ven, the model check was mainly due to a lack
of testing on systems before INTEL_CORE2_MEROM. He suggests considering
all Intel processors as having an efficient idle.

Extend the IO busy classification to all Intel processors starting with
Family 6, including Family 15 (Pentium 4s) and upcoming Families 18/19.

Use an x86 VFM check and move the function to the header file to avoid
using arch-specific #ifdefs in the C file.

Signed-off-by: Sohil Mehta <sohil.mehta@intel.com>
Link: https://patch.msgid.link/20250908230655.2562440-1-sohil.mehta@intel.com
[ rjw: Added empty line after #include ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>