Automatically disable x2APIC mode on SandyBridge Lenovo machines. I
believe that the bug only affects mobile CPUs, at least I did not see
other reports, but it is impossible to detect it in madt_setup_local().

While there, reduce duplication in the information strings printed
when x2APIC is auto-disabled, and do not print the line when user
manually override the setting.

Tested and reviewed by: royger (previous version)
Sponsored by: The FreeBSD Foundation