delay_timer: correct sparse issues and warnings

Use NULL instead of 0 where required.
Include headers to have the prototype of the functions.
Signed-off-by: Yann Gautier <yann.gautier@st.com>
Signed-off-by: Etienne Carriere <etienne.carriere@st.com>

drivers/delay_timer/delay_timer.c

@@ -19,10 +19,10 @@ static const timer_ops_t *ops;
  ***********************************************************/
 void udelay(uint32_t usec)
 {
-	assert(ops != 0 &&
+	assert(ops != NULL &&
 		(ops->clk_mult != 0) &&
 		(ops->clk_div != 0) &&
-		(ops->get_timer_value != 0));
+		(ops->get_timer_value != NULL));
 
 	uint32_t start, delta, total_delta;
 
@@ -57,10 +57,10 @@ void mdelay(uint32_t msec)
  ***********************************************************/
 void timer_init(const timer_ops_t *ops_ptr)
 {
-	assert(ops_ptr != 0  &&
+	assert(ops_ptr != NULL  &&
 		(ops_ptr->clk_mult != 0) &&
 		(ops_ptr->clk_div != 0) &&
-		(ops_ptr->get_timer_value != 0));
+		(ops_ptr->get_timer_value != NULL));
 
 	ops = ops_ptr;
 }

drivers/delay_timer/generic_delay_timer.c

@@ -9,6 +9,7 @@
 #include <bl_common.h>
 #include <debug.h>
 #include <delay_timer.h>
+#include <generic_delay_timer.h>
 #include <platform.h>
 
 /* Ticks elapsed in one second by a signal of 1 MHz */