ARM platforms: Add support for EL3 TZC memory region

Some recent enhancements to EL3 runtime firmware like support for
save and restoring GICv3 register context during system_suspend
necessitates additional data memory for the firmware. This patch
introduces support for creating a TZC secured DDR carveout for use
by ARM reference platforms. A new linker section `el3_tzc_dram` is
created using platform supplied linker script and data marked with
the attribute `arm_el3_tzc_dram` will be placed in this section.
The FVP makefile now defines the `PLAT_EXTRA_LD_SCRIPT` variable to
allow inclusion of the platform linker script by the top level BL31
linker script.

Change-Id: I0e7f4a75a6ac51419c667875ff2677043df1585d
Signed-off-by: Soby Mathew <soby.mathew@arm.com>
diff --git a/include/plat/arm/common/arm_common.ld.S b/include/plat/arm/common/arm_common.ld.S
new file mode 100644
index 0000000..478b08c
--- /dev/null
+++ b/include/plat/arm/common/arm_common.ld.S
@@ -0,0 +1,28 @@
+/*
+ * Copyright (c) 2017, ARM Limited and Contributors. All rights reserved.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+#ifndef __ARM_COMMON_LD_S__
+#define __ARM_COMMON_LD_S__
+
+MEMORY {
+    EL3_SEC_DRAM (rw): ORIGIN = ARM_EL3_TZC_DRAM1_BASE, LENGTH = ARM_EL3_TZC_DRAM1_SIZE
+}
+
+SECTIONS
+{
+	. = ARM_EL3_TZC_DRAM1_BASE;
+	ASSERT(. == ALIGN(4096),
+	"ARM_EL3_TZC_DRAM_BASE address is not aligned on a page boundary.")
+	el3_tzc_dram (NOLOAD) : ALIGN(4096) {
+	__EL3_SEC_DRAM_START__ = .;
+	*(arm_el3_tzc_dram)
+	__EL3_SEC_DRAM_UNALIGNED_END__ = .;
+
+	. = NEXT(4096);
+	__EL3_SEC_DRAM_END__ = .;
+	} >EL3_SEC_DRAM
+}
+
+#endif /* __ARM_COMMON_LD_S__ */