Add support for BL2 in XIP memory

In some use-cases BL2 will be stored in eXecute In Place (XIP) memory,
like BL1. In these use-cases, it is necessary to initialize the RW sections
in RAM, while leaving the RO sections in place. This patch enable this
use-case with a new build option, BL2_IN_XIP_MEM. For now, this option
is only supported when BL2_AT_EL3 is 1.

Signed-off-by: Jiafei Pan <Jiafei.Pan@nxp.com>
diff --git a/include/common/aarch64/el3_common_macros.S b/include/common/aarch64/el3_common_macros.S
index 4ebf77b..e85249c 100644
--- a/include/common/aarch64/el3_common_macros.S
+++ b/include/common/aarch64/el3_common_macros.S
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2015-2017, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2015-2018, ARM Limited and Contributors. All rights reserved.
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -294,7 +294,7 @@
 		bl	zeromem
 #endif
 
-#ifdef IMAGE_BL1
+#if defined(IMAGE_BL1) || (defined(IMAGE_BL2) && BL2_IN_XIP_MEM)
 		ldr	x0, =__DATA_RAM_START__
 		ldr	x1, =__DATA_ROM_START__
 		ldr	x2, =__DATA_SIZE__