perf kvm/{x86,s390}: Remove dependency on uapi/kvm_perf.h

perf kvm/{x86,s390}: Remove dependency on uapi/kvm_perf.h

Its better to remove the dependency on uapi/kvm_perf.h to allow dynamic
discovery of kvm events (if its needed). To do this, some extern
variables have been introduced with which we can keep the generic
functions generic.

Signed-off-by: Hemant Kumar <hemant@linux.vnet.ibm.com>
Acked-by: Alexander Yarygin <yarygin@linux.vnet.ibm.com>
Acked-by: David Ahern <dsahern@gmail.com>
Cc: Michael Ellerman <mpe@ellerman.id.au>
Cc: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Scott  Wood <scottwood@freescale.com>
Cc: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: linuxppc-dev@lists.ozlabs.org
Link: http://lkml.kernel.org/r/1453962787-15376-1-git-send-email-hemant@linux.vnet.ibm.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>