secure_tc: enable branch protection

Setting branch_protection to standard will enable PAC and BTI for the
Total Compute platform.

Signed-off-by: Davidson K <davidson.kumaresan@arm.com>
Change-Id: If40c401db876eb6f39802bb57331b1f7c368a0b0
diff --git a/BUILD.gn b/BUILD.gn
index 159ce0d..5b0911c 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -283,6 +283,7 @@
   heap_pages = 180
   max_cpus = 8
   max_vms = 16
+  branch_protection = "standard"
   toolchain_args = {
     plat_ffa = "//src/arch/aarch64/plat/ffa:spmc"
     plat_psci = "//src/arch/aarch64/plat/psci:spmc"