fix(zynqmp): do not export apu_ipi

apu_ipi structure is not used anywhere externally that's why make it
static.

Change-Id: Icfa99e16ae36fcbcc83b0891aa3527993d49c7ed
Signed-off-by: Michal Simek <michal.simek@amd.com>
diff --git a/plat/xilinx/zynqmp/pm_service/pm_client.c b/plat/xilinx/zynqmp/pm_service/pm_client.c
index 2c7834d..fd6adec 100644
--- a/plat/xilinx/zynqmp/pm_service/pm_client.c
+++ b/plat/xilinx/zynqmp/pm_service/pm_client.c
@@ -35,9 +35,7 @@
 
 DEFINE_BAKERY_LOCK(pm_client_secure_lock);
 
-extern const struct pm_ipi apu_ipi;
-
-const struct pm_ipi apu_ipi = {
+static const struct pm_ipi apu_ipi = {
 	.local_ipi_id = IPI_ID_APU,
 	.remote_ipi_id = IPI_ID_PMU0,
 	.buffer_base = IPI_BUFFER_APU_BASE,