phb5: Fix PHB max link speed definition on P10
phb5: Fix PHB max link speed definition on P10

Not all PHBs are capable of GEN5 speed on P10. In all PEC
configurations, the first PHB is the only one which can handle GEN5.

Signed-off-by: Frederic Barrat <c90240987c583ac0802fbeb88cb1684edc683e18@linux.ibm.com>
Signed-off-by: Vasant Hegde <a6d753843573f7bfed5075c1e875b0be8007a0ab@linux.vnet.ibm.com>

qemu/skiboot,open-power/skiboot,qemu/skiboot,open-power/skiboot,legoater/skiboot,shenki/skiboot,legoater/skiboot,legoater/skiboot,qemu/skiboot,legoater/skiboot,shenki/skiboot,open-power/skiboot,open-power/skiboot,open-power/skiboot,legoater/skiboot,qemu/skiboot,qemu/skiboot,shenki/skiboot,shenki/skiboot,shenki/skiboot