Use standard errno definitions in load_auth_image()

This patch replaces custom definitions used as return values for
the load_auth_image() function with standard error codes defined
in errno.h. The custom definitions have been removed.

It also replaces the usage of IO framework error custom definitions,
which have been deprecated. Standard errno definitions are used
instead.

Change-Id: I1228477346d3876151c05b470d9669c37fd231be
diff --git a/bl2/bl2_main.c b/bl2/bl2_main.c
index 71940a6..404744b 100644
--- a/bl2/bl2_main.c
+++ b/bl2/bl2_main.c
@@ -34,6 +34,7 @@
 #include <auth_mod.h>
 #include <bl_common.h>
 #include <debug.h>
+#include <errno.h>
 #include <platform.h>
 #include <platform_def.h>
 #include <stdint.h>
@@ -239,7 +240,7 @@
 
 	e = load_bl32(bl2_to_bl31_params);
 	if (e) {
-		if (e == LOAD_AUTH_ERR) {
+		if (e == -EAUTH) {
 			ERROR("Failed to authenticate BL3-2\n");
 			panic();
 		} else {