boards: spresense: Support board_reset on interrupt context

When CONFIG_BOARD_RESET_ON_ASSERT is enabled, board_reset() may be
called on interrupt context. This commit changes to be able to call the
function on interrupt context.

boards/arm/cxd56xx/spresense/src/cxd56_power.c

@@ -509,9 +509,12 @@ int board_reset(int status)
 {
   /* Restore the original state for bootup after power cycle  */
 
+  if (!up_interrupt_context())
+    {
       board_xtal_power_control(true);
       board_flash_power_control(true);
       up_pm_acquire_freqlock(&g_hv_lock);
+    }
 
   /* System reboot */