libpayload: Add support for arm64 in libpayload

Basic support for arm64 is enabled in libpayload.
Features added:
1) mem* operations in assembly.
2) Basic exception handling and support for testing exceptions.
3) Caching support.

Tested with arm64-generic board compilation.

BUG=None
BRANCH=None
TEST=Compilation successful

Original-Change-Id: I4e86301f9c6383abc078e2b70071fb84bd6e4741
Original-Signed-off-by: Furquan Shaikh <furquan@google.com>
Original-Reviewed-on: https://chromium-review.googlesource.com/187067
Original-Tested-by: Furquan Shaikh <furquan@chromium.org>
Original-Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Original-Commit-Queue: Furquan Shaikh <furquan@chromium.org>
(cherry picked from commit a70d13f3d225535843ab352290eab2e1ec7a9b4b)
Signed-off-by: Marc Jones <marc.jones@se-eng.com>

Change-Id: Ie3affe6a2bdd4fed3058de739d4c6aa573e5b251
Reviewed-on: http://review.coreboot.org/8063
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
Reviewed-by: Furquan Shaikh <furquan@google.com>

payloads/libpayload/util/xcompile/xcompile

@@ -111,6 +111,11 @@ detect_special_flags() {
 			#	CFLAGS="$CFLAGS -mcpu=cortex-a9"
 			;;
 	esac
+
+	case "$architecture" in
+		arm64-generic )
+			;;
+	esac
 }
 
 report_arch_toolchain() {
@@ -135,7 +140,7 @@ touch "$TMPFILE"
 trap clean_up EXIT
 
 # Architecture definition
-SUPPORTED_ARCHITECTURE="x86 arm"
+SUPPORTED_ARCHITECTURE="x86 arm arm64"
 
 # ARM Architecture
 TARCH_arm="arm"
@@ -143,6 +148,12 @@ TBFDARCH_arm="littlearm"
 TCLIST_arm="armv7a armv7-a"
 TWIDTH_arm="32"
 
+# ARM64 Architecture
+TARCH_arm64="arm64"
+TBFDARCH_arm64="littleaarch64"
+TCLIST_arm64="aarch64"
+TWIDTH_arm64="64"
+
 # X86 Architecture
 TARCH_x86="i386"
 TBFDARCH_x86="i386"