scsi: add persistent reservation manager using qemu-pr-helper

This adds a concrete subclass of pr-manager that talks to qemu-pr-helper.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
diff --git a/scsi/Makefile.objs b/scsi/Makefile.objs
index 5496d2a..4d25e47 100644
--- a/scsi/Makefile.objs
+++ b/scsi/Makefile.objs
@@ -1,3 +1,3 @@
 block-obj-y += utils.o
 
-block-obj-$(CONFIG_LINUX) += pr-manager.o
+block-obj-$(CONFIG_LINUX) += pr-manager.o pr-manager-helper.o