fix(tc): Change gic version to 4

Confirmed FVP_TC0 has GICv4.1 functionality enabled by default.

Signed-off-by: Madhukar Pappireddy <madhukar.pappireddy@arm.com>
Change-Id: I536a328289f6618b8ea3026654d0eb2412845d4d
diff --git a/BUILD.gn b/BUILD.gn
index 6027292..a308cee 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -251,7 +251,7 @@
   boot_flow = "//src/boot_flow:spmc"
   console = "//src/arch/aarch64/pl011"
   iommu = "//src/iommu:absent"
-  gic_version = 3
+  gic_version = 4
   gicd_base_address = "0x30000000"
   gicr_base_address = "0x30080000"
   heap_pages = 60