feat(fvp): add plat API to set and get the DRTM error

Added a platform function to set and get DRTM error.
Also, added a platform function to reset the system.

Signed-off-by: Manish V Badarkhe <Manish.Badarkhe@arm.com>
Change-Id: I471f2387f8c78b21a06af063a6fa02cda3646557
diff --git a/plat/arm/common/arm_err.c b/plat/arm/common/arm_err.c
index f80ba78..fa36e8d 100644
--- a/plat/arm/common/arm_err.c
+++ b/plat/arm/common/arm_err.c
@@ -13,3 +13,8 @@
 {
 	plat_arm_error_handler(err);
 }
+
+void __dead2 plat_system_reset(void)
+{
+	plat_arm_system_reset();
+}