KVM: Get rid of kvm_kvfree()

kvm_kvfree() provides exactly the same functionality as the
new common kvfree() function - so let's simply replace the
kvm function with the common function.

Signed-off-by: Thomas Huth <thuth@linux.vnet.ibm.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>