fix(bti): Add branch protection to VHE builds

This patch enables branch protection for builds that enable VHE.

Signed-off-by: Raghu Krishnamurthy <raghu.ncstate@gmail.com>
Change-Id: Ib32b753d6cc2f3263abb7c51590198839b26b272
diff --git a/BUILD.gn b/BUILD.gn
index 8b1c66b..2c4fca7 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -108,6 +108,7 @@
   heap_pages = 60
   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"
@@ -153,6 +154,7 @@
   heap_pages = 60
   max_cpus = 8
   max_vms = 16
+  branch_protection = "standard"
   toolchain_args = {
     plat_ffa = "//src/arch/aarch64/plat/ffa:hypervisor"
     pl011_base_address = "0x1c090000"