lguest: add operations to get/set a register from the Launcher.

We use the ptrace API struct, and we currently don't let them set
anything but the normal registers (we'd have to filter the others).

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
diff --git a/include/linux/lguest_launcher.h b/include/linux/lguest_launcher.h
index 495203f..f27cae2 100644
--- a/include/linux/lguest_launcher.h
+++ b/include/linux/lguest_launcher.h
@@ -63,6 +63,8 @@
 	LHREQ_IRQ, /* + irq */
 	LHREQ_BREAK, /* No longer used */
 	LHREQ_EVENTFD, /* + address, fd. */
+	LHREQ_GETREG, /* + offset within struct pt_regs (then read value). */
+	LHREQ_SETREG, /* + offset within struct pt_regs, value. */
 };
 
 /*