clocksource: vf_pit_timer: Support shutdown mode

In order to avoid waking up the system in a low power mode, the
clocksource should not generate interrupts anymore. Disable the PIT
timer interrupt when changing into the CLOCK_EVT_MODE_SHUTDOWN mode.

[dlezcano] : remove superfluous empty line

Signed-off-by: Stefan Agner <[e-mail]>
Signed-off-by: Daniel Lezcano <[e-mail]>
Acked-by: Bill Pringlemeir <[e-mail]>

drivers/clocksource/vf_pit_timer.c

···
 	case CLOCK_EVT_MODE_PERIODIC:
 		pit_set_next_event(cycle_per_jiffy, evt);
 		break;
+	case CLOCK_EVT_MODE_SHUTDOWN:
+	case CLOCK_EVT_MODE_UNUSED:
+		pit_timer_disable();
+		break;
 	default:
 		break;
 	}