This makes x86-64 use the common X86_PM_TIMER Kconfig entry in drivers/acpi

And since PM timer is needed for correct timing on a lot of systems
now (e.g. AMD dual cores) and we often get bug reports from people
who forgot to set it make it depend on CONFIG_EMBEDDED. x86-64 had
this change before and it's a good thing.

I also fixed the description slightly to make this more clear.

Cc: len.brown@intel.com
Signed-off-by: NAndi Kleen <ak@suse.de>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>