HV: re-arch boot component header

The patch re-arch boot component header files by:

- moving multiboot.h from include/arch/x86/ to boot/include/ and keep
  this header for multiboot1 protocol data struct only;

- moving multiboot related MACROs in cpu_primary.S to multiboot.h;

- creating an independent boot.h to store acrn specific boot information
  for other files' reference;

Tracked-On: #4419

Signed-off-by: Victor Sun <victor.sun@intel.com>
Acked-by: Eddie Dong <eddie.dong@intel.com>

hypervisor/boot/include/boot.h

@@ -0,0 +1,17 @@
+/*
+ * Copyright (C) 2020 Intel Corporation. All rights reserved.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+#ifndef BOOT_H_
+#define BOOT_H_
+
+#include <multiboot.h>
+
+#define MAX_BOOTARGS_SIZE		2048U
+
+/* boot_regs store the multiboot info magic and address */
+extern uint32_t boot_regs[2];
+
+#endif /* BOOT_H_ */