x86 msr-index: define MSR_TURBO_RATIO_LIMIT,1,2

MSR_TURBO_RATIO_LIMIT has grown into a set of three registers.
Add the documented names for them, in preparation
for deleting the previous ad-hoc names:

+#define MSR_TURBO_RATIO_LIMIT          0x000001ad
+#define MSR_TURBO_RATIO_LIMIT1         0x000001ae
+#define MSR_TURBO_RATIO_LIMIT2         0x000001af

Signed-off-by: Len Brown <len.brown@intel.com>
Cc: x86@kernel.org