arm720t: add back common.h include

Add back common.h header that was removed in previous patch so that
CONFIG_TEGRA can be evaluated correctly.

Signed-off-by: Allen Martin <amartin@nvidia.com>
Signed-off-by: Tom Warren <twarren@nvidia.com>

arch/arm/cpu/arm720t/interrupts.c

@@ -26,6 +26,8 @@
  * MA 02111-1307 USA
  */
 
+#include <common.h>
+
 #ifdef CONFIG_USE_IRQ
 void do_irq (struct pt_regs *pt_regs)
 {