Include debug.h in debug.S

debug.S was using macros defined in debug.h, but since it didn't
include it, these macros were taking the value 0, which means that
all the preprocessor conditionals were wrong.

Change-Id: If4ca81cc5a1662991589f914a2557ceff0eaaede
Signed-off-by: Roberto Vargas <roberto.vargas@arm.com>

common/aarch64/debug.S

@@ -6,6 +6,7 @@
 
 #include <arch.h>
 #include <asm_macros.S>
+#include <debug.h>
 
 	.globl	asm_print_str
 	.globl	asm_print_hex