drivers: timer: provide timer irq to tests

As with previous commit, make the timer irq a simple integer variable
exported by the timer driver for the benefit of this one test
(tests/kernel/context).

Signed-off-by: Anas Nashif <anas.nashif@intel.com>
diff --git a/drivers/timer/esp32c3_sys_timer.c b/drivers/timer/esp32c3_sys_timer.c
index fed61c2..bc8a7e7 100644
--- a/drivers/timer/esp32c3_sys_timer.c
+++ b/drivers/timer/esp32c3_sys_timer.c
@@ -25,6 +25,10 @@
 #define MAX_TICKS ((MAX_CYC - CYC_PER_TICK) / CYC_PER_TICK)
 #define MIN_DELAY 1000
 
+#if defined(CONFIG_TEST)
+const int32_t z_sys_timer_irq_for_test = DT_IRQN(DT_NODELABEL(systimer0));
+#endif
+
 #define TICKLESS IS_ENABLED(CONFIG_TICKLESS_KERNEL)
 
 static struct k_spinlock lock;