revision 300037 broke stable/9 kernel build for amd64

[Eugene Grosbein]

Hi!

https://svnweb.freebsd.org/base?view=revision&revision=300037
https://svnweb.freebsd.org/base/stable/9/sys/amd64/amd64/initcpu.c?view=patch&r1=300037&r2=300036&pathrev=300037

This patch uses symbol MSR_NB_CFG1 that's not defined for stable/9 breaking kernel build.
Please repair.

Eugene Grosbein