x86: Rename turbo ratio MSR to MSR_TURBO_RATIO_LIMIT

This MSR number is used on most modern Intel processors, so drop the
confusing NHM prefix (which might mean Nehalem).

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
[bmeng: drop MSR_IVT_TURBO_RATIO_LIMIT as no code uses it]
Signed-off-by: Bin Meng <bmeng.cn@gmail.com>