[coreboot] AMD HT link frequency limit configuration patch

[Timothy Pearson]

This patch allows the user to select a maximum HyperTransport link frequency.

Speed capping is required for maximum stability when attempting to use new
HT3 CPUs on older HT1 mainboards, as the physical inter-CPU traces on the
mainboard may not be able to reliably handle the faster HT3 link
frequency.

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Signed-off-by: Timothy Pearson

Timothy Pearson
Raptor Engineering