tracing, kvm: change MARKERS to select instead of depends on

Impact: build fix

fix:

 kernel/trace/Kconfig:42:error: found recursive dependency: TRACING ->
 TRACEPOINTS -> MARKERS -> KVM_TRACE -> RELAY -> KMEMTRACE -> TRACING

markers is a facility that should be selected - not depended on
by an interactive Kconfig entry.

Signed-off-by: Ingo Molnar <mingo@elte.hu>