latencytop: Change Kconfig dependency.

Change latencytop Kconfig entry so it doesn't list the archictectures
that support it. Instead introduce HAVE_LATENCY_SUPPORT which any
architecture can set. Should reduce patch conflicts.

Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Holger Wolf <wolf@linux.vnet.ibm.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>