lguest: map Switcher text whenever we allocate a new pagetable.

It's always to same, so no need to put in the PTE every time we're
about to run.  Keep a flag to track whether the pagetable has the
Switcher entries allocated, and when allocating always initialize the
Switcher text PTE.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

drivers/lguest/lg.h

@@ -16,6 +16,7 @@
 
 struct pgdir {
 	unsigned long gpgdir;
+	bool switcher_mapped;
 	pgd_t *pgdir;
 };