cpu/intel/model_206ax: Add overclocking support

Add a Kconfig option to force Turbo Ratio values to the maximum possible
value, which is the maximum non-turbo ratio plus the number of OC bins.
The OC bins value comes from the FLEX_RATIO MSR bits 19..17 and is the
maximum allowed difference between the max turbo and non-turbo ratios.
The relevant MSRs are documented in the non-public BIOS Writer's Guide.

If the number of OC bins is seven, it indicates that the CPU is unlocked
and can use even higher multiplier ratios. Due to lack of hardware, this
was not implemented. Plus, it would require a recovery mechanism should
the requested multiplier render the computer unable to boot correctly.
So, unlocked CPUs are treated like limited overclocking-capable parts.

Normally, Turbo Boost uses higher ratios when less CPU cores are active.
With this option, one can force the CPU to use the maximum turbo ratio
for any number of active CPU cores, effectively running the CPU faster.
Please make sure your thermal solution can handle the extra heat output!

Tested on Asus P8Z77-V LX2 with an i7-2600 and an i5-3330, by checking
the output of `cat /proc/cpuinfo` with all CPU threads under load:

- i7-2600: 34 max non-turbo ratio + 4 OC bins = 38 max turbo ratio.
- i5-3330: 30 max non-turbo ratio + 4 OC bins = 34 max turbo ratio.

Change-Id: I60bef32bfdde3c32a11f07afff64fc83d65fd3f1
Signed-off-by: Angel Pons <th3fanbus@gmail.com>
---
M src/cpu/intel/model_206ax/Kconfig
M src/cpu/intel/model_206ax/model_206ax.h
M src/cpu/intel/model_206ax/model_206ax_init.c
3 files changed, 67 insertions(+), 0 deletions(-)