xive/p9: introduce header files for the registers

This is moving the definitions of the registers of the P9 XIVE
interrupt controller and the P9 XIVE internal structures in a specific
header file and moving the definitions related to the thread interrupt
context area to a common file.

Signed-off-by: Cédric Le Goater <clg@kaod.org>
Signed-off-by: Oliver O'Halloran <oohall@gmail.com>

hw/xive.c

@@ -1,15 +1,17 @@
 // SPDX-License-Identifier: Apache-2.0
 /*
- * XIVE - P9 interrupt controller
+ * XIVE: eXternal Interrupt Virtualization Engine. POWER9 interrupt
+ * controller
  *
- * Copyright 2016-2019 IBM Corp.
+ * Copyright (c) 2016-2019, IBM Corporation.
  */
 
 #include <skiboot.h>
 #include <xscom.h>
 #include <chip.h>
 #include <io.h>
 #include <xive.h>
+#include <xive-p9-regs.h>
 #include <xscom-p9-regs.h>
 #include <interrupts.h>
 #include <timebase.h>