Remove direct usage of __attribute__((foo))

Migrate all direct usage of __attribute__ to usage of their
corresponding macros from cdefs.h.
e.g.:
 - __attribute__((unused)) -> __unused

Signed-off-by: Soren Brinkmann <soren.brinkmann@xilinx.com>
diff --git a/lib/aarch64/xlat_tables.c b/lib/aarch64/xlat_tables.c
index fa1a03d..b00dc0b 100644
--- a/lib/aarch64/xlat_tables.c
+++ b/lib/aarch64/xlat_tables.c
@@ -58,7 +58,7 @@
 __aligned(NUM_L1_ENTRIES * sizeof(uint64_t));
 
 static uint64_t xlat_tables[MAX_XLAT_TABLES][XLAT_TABLE_ENTRIES]
-__aligned(XLAT_TABLE_SIZE) __attribute__((section("xlat_table")));
+__aligned(XLAT_TABLE_SIZE) __section("xlat_table");
 
 static unsigned next_xlat;
 static unsigned long max_pa;