remove empty definition of display_boot_progress()

This patch replaces the empty definition of display_boot_progress() in
bl2_main.c with a weak definition. The former allowed bl2 to use the
early_exceptions(). It is possible to do that with a simple weak
definition as well.

Change-Id: Idb3f425a5e265f3579b638e3d26bd8c9bb78f80d
diff --git a/bl1/aarch64/early_exceptions.S b/bl1/aarch64/early_exceptions.S
index d2e65b0..bc3e946 100644
--- a/bl1/aarch64/early_exceptions.S
+++ b/bl1/aarch64/early_exceptions.S
@@ -35,7 +35,7 @@
 #include <runtime_svc.h>
 
 	.globl	early_exceptions
-
+	.weak	display_boot_progress
 
 	.section	.text, "ax"; .align 11
 
@@ -214,3 +214,15 @@
 	mov	x0, #SERROR_AARCH32
 	bl	plat_report_exception
 	b	SErrorA32
+
+	.align	7
+	/* -----------------------------------------------------
+	 * BL1 redefines this function to print the fact that
+	 * BL2 has done its job and BL31 is about to be loaded.
+	 * This weak definition allows other bootloader stages
+	 * to use the 'early_exceptions' without running into
+	 * compilation errors.
+	 * -----------------------------------------------------
+	 */
+display_boot_progress:
+	ret