fix(versal): add external declaration

This corrects the MISRA violation C2012-8.4:
A compatible declaration shall be visible when an object or
function with external linkage is defined.

Change-Id: I91817596c5de84b259a5dffcc01a7b1106a5b7a4
Signed-off-by: Maheedhar Bollapalli <maheedharsai.bollapalli@amd.com>
diff --git a/plat/xilinx/versal/include/plat_private.h b/plat/xilinx/versal/include/plat_private.h
index 4b2b6cf..658dc9e 100644
--- a/plat/xilinx/versal/include/plat_private.h
+++ b/plat/xilinx/versal/include/plat_private.h
@@ -34,6 +34,8 @@
 void plat_versal_gic_pcpu_init(void);
 void plat_versal_gic_save(void);
 void plat_versal_gic_resume(void);
+void plat_versal_gic_redistif_on(void);
+void plat_versal_gic_redistif_off(void);
 
 uint32_t versal_calc_core_pos(u_register_t mpidr);
 /*