kvm: Add a new machine option kvm-type

Targets like ppc64 support different types of KVM, one which use
hypervisor mode and the other which doesn't. Add a new machine
option kvm-type that helps in selecting the respective ones
We also add a new QEMUMachine callback get_vm_type that helps
in mapping the string representation of kvm type specified.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
[agraf: spelling fixes, use error_report(), use qemumachine.h]
Signed-off-by: Alexander Graf <agraf@suse.de>
diff --git a/qtest.c b/qtest.c
index ae941d6..0ac9f42 100644
--- a/qtest.c
+++ b/qtest.c
@@ -500,7 +500,7 @@
     }
 }
 
-int qtest_init_accel(void)
+int qtest_init_accel(QEMUMachine *machine)
 {
     configure_icount("0");