xen/riscv: setup initial pagetables

The patch does two thing:
1. Setup initial pagetables.
2. Enable MMU which end up with code in
   cont_after_mmu_is_enabled()

Signed-off-by: Oleksii Kurochko <oleksii.kurochko@gmail.com>
Acked-by: Bobby Eshleman <bobbyeshleman@gmail.com>

xen/arch/riscv/setup.c

@@ -21,7 +21,10 @@ void __init noreturn start_xen(unsigned long bootcpu_id,
 {
     early_printk("Hello from C env\n");
 
-    early_printk("All set up\n");
+    setup_initial_pagetables();
+
+    enable_mmu();
+
     for ( ;; )
         asm volatile ("wfi");