feat(zynqmp): enable assertion

Retain assertions in builds for TF-A run from DDR with
ENABLE_ASSERTIONS=1. It helps to catch programming errors
(e.g. bad argument provided by platform porting function)
code size change is 4k.
For debug builds, assertions are enabled by default.
The same change is done by Tegra: plat/nvidia/tegra/platform.mk.

Change-Id: I1790862616faddf68b4d533750722dad27cae269
Signed-off-by: Amit Nagal <amit.nagal@amd.com>
diff --git a/plat/xilinx/zynqmp/platform.mk b/plat/xilinx/zynqmp/platform.mk
index b778932..e266615 100644
--- a/plat/xilinx/zynqmp/platform.mk
+++ b/plat/xilinx/zynqmp/platform.mk
@@ -49,6 +49,10 @@
     ifdef ZYNQMP_ATF_MEM_PROGBITS_SIZE
         $(eval $(call add_define,ZYNQMP_ATF_MEM_PROGBITS_SIZE))
     endif
+
+    # enable assert() when TF-A runs from DDR memory.
+    ENABLE_ASSERTIONS := 1
+
 endif
 
 ifdef ZYNQMP_BL32_MEM_BASE