x86, cpu: Move AMD Elan Kconfig under "Processor family"

Currently the option resides under X86_EXTENDED_PLATFORM due to historical
nonstandard A20M# handling. However that is no longer the case and so Elan can
be treated as part of the standard processor choice Kconfig option.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Link: http://lkml.kernel.org/r/1302245177.31620.47.camel@localhost.localdomain
Cc: H. Peter Anvin <hpa@zytor.com>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>