amlogic: Fix header guards

Make the header guards more generic and contextually remove the
GXBB_BL31_PLAT_PARAM_VAL value that is unused on the GXL platform.

Signed-off-by: Carlo Caione <ccaione@baylibre.com>
Change-Id: I842fa2e084e71280ae17b39c67877e844821a171
diff --git a/plat/amlogic/gxl/gxl_def.h b/plat/amlogic/gxl/gxl_def.h
index 1af101e..6f49ed2 100644
--- a/plat/amlogic/gxl/gxl_def.h
+++ b/plat/amlogic/gxl/gxl_def.h
@@ -4,8 +4,8 @@
  * SPDX-License-Identifier: BSD-3-Clause
  */
 
-#ifndef GXBB_DEF_H
-#define GXBB_DEF_H
+#ifndef GXL_DEF_H
+#define GXL_DEF_H
 
 #include <lib/utils_def.h>
 
@@ -125,4 +125,4 @@
 #define AML_JTAG_A53_AO				U(2)
 #define AML_JTAG_A53_EE				U(3)
 
-#endif /* GXBB_DEF_H */
+#endif /* GXL_DEF_H */