xen: Port Xen hypervisor related code from mini-os

Port hypervisor related code from Mini-OS. This is referencing the code
of Mini-OS from [1] by Huang Shijie and Volodymyr Babchuk which is for
ARM64.
Update essential arch code to support required bit operations, memory
barriers etc.

Copyright for the bits ported belong to at least the following authors,
please see related files for details:

Copyright (c) 2002-2003, K A Fraser
Copyright (c) 2005, Grzegorz Milos, gm281@cam.ac.uk,Intel Research Cambridge
Copyright (c) 2014, Karim Allah Ahmed <karim.allah.ahmed@gmail.com>

[1] - https://github.com/zyzii/mini-os.git

Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
Signed-off-by: Anastasiia Lukianenko <anastasiia_lukianenko@epam.com>
[trini: Drop wmb() from musb-net/linux-compat.h now]
Signed-off-by: Tom Rini <trini@konsulko.com>

common/board_r.c

@@ -56,6 +56,9 @@
 #include <timer.h>
 #include <trace.h>
 #include <watchdog.h>
+#ifdef CONFIG_XEN
+#include <xen.h>
+#endif
 #ifdef CONFIG_ADDR_MAP
 #include <asm/mmu.h>
 #endif
@@ -465,6 +468,13 @@ static int initr_mmc(void)
 }
 #endif
 
+#ifdef CONFIG_XEN
+static int initr_xen(void)
+{
+	xen_init();
+	return 0;
+}
+#endif
 /*
  * Tell if it's OK to load the environment early in boot.
  *
@@ -761,6 +771,9 @@ static init_fnc_t init_sequence_r[] = {
 #endif
 #ifdef CONFIG_MMC
 	initr_mmc,
+#endif
+#ifdef CONFIG_XEN
+	initr_xen,
 #endif
 	initr_env,
 #ifdef CONFIG_SYS_BOOTPARAMS_LEN