x86 Kconfig: change X86_MINIMUM_CPU_MODEL to X86_MINIMUM_CPU_FAMILY

The X86_MINIMUM_CPU_MODEL name isn't really right, so change it to
X86_MINIMUM_CPU_FAMILY.  Also, the default minimum should be 3, not 0.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>